Legion I. SPUMELLARIA, (continued 12)

Genus 196. Lithocyclia,^[235] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Coccodiscida with simple circular margin of the disk, without radial appendages. Medullary shell simple.

The genus Lithocyclia is the most simple form of Coccodiscida, and represents the common ancestral form of this family, from which all other genera of it can be derived. The lenticular, biconvex disk is quite simple, composed of a variable number of concentric, circular, chambered rings, which are pierced by radial beams, and which surround the circular lenticular cortical shell or "phacoid shell." The latter contains a simple spherical medullary shell in its centre, and is connected with it by radial beams. The margin of the disk is circular, quite simple, without radial spines or chambered arms.

1. Lithocyclia cingulata, n. sp.

Phacoid shell (or lenticular porous cortical shell) three times as broad as the spherical enclosed medullary shell, surrounded by one single chambered girdle or ring (with about forty chambers of equal size, separated by radial beams). Margin of the disk circular, smooth. Pores of the convex covering plates regular, circular; eight on the radius of the phacoid shell, two on the breadth of the ring.

Dimensions.—Diameter of the disk (with one ring) 0.13, of the phacoid shell 0.1, of the medullary shell 0.033.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Lithocyclia lenticula, n. sp. (Pl. 36, figs. 3, 4).

Phacoid shell two and a half times as broad as the enclosed medullary shell, surrounded by three chambered girdles of equal size, which are divided by piercing radial beams each into about fifty chambers. Margin of the disk thorny. Pores irregular, roundish; seven on the radius of the phacoid shell, two on the breadth of each girdle.

Dimensions.—Diameter of the disk (with three girdles) 0.2, of the phacoid shell 0.11, of the medullary shell 0.045.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Lithocyclia ocellus, Ehrenberg.

Lithocyclia ocellus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 30; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxix. fig. 3.

Phacoid shell three times as broad as the medullary shell, surrounded by numerous (seven to eleven) chambered rings, which are divided by piercing radial beams each into sixty to ninety chambers. Margin of the disk smooth. Pores regular, circular; nine on the radius of the phacoid shell, one single pore on each chamber.

Dimensions.—Diameter of the disk (with eleven rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.035.

Habitat.—Fossil in the rocks of Barbados.

4. Lithocyclia monococcus, n. sp.

Stephanopyxis dubiosa (?), Bury, 1862, Polycystins of Barbados, pl. xiii. figs. 1, 2.

Phacoid shell four times as broad as the medullary shell, surrounded by numerous (five to eight) chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk thickened, thorny. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber.

Dimensions.—Diameter of the disk (with eight rings) 0.18, of the phacoid shell 0.12, of the medullary shell 0.03.

Habitat.—Pacific, central area, Station 267, depth 2700 fathoms; also fossil in the rocks of Barbados.

5. Lithocyclia heteropora, n. sp.

Phacoid shell two and a third times as broad as the medullary shell, surrounded by five to nine chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk smooth. Pores very different in the inner and outer part of the surface; in the phacoid shell larger, regular, circular, eight on its radius, in the chambered periphery very small and irregular, somewhat spongy.

Dimensions.—Diameter of the disk (with nine rings) 0.2, of the phacoid shell 0.13, of the medullary shell 0.055.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Genus 197. Coccodiscus,^[236] Haeckel, 1862, Monogr. d. Radiol., p. 485.

Definition.—Coccodiscida with simple circular margin of the disk, without radial appendages. Medullary shell double.

The genus Coccodiscus has quite the same form and structure as the preceding Lithocyclia, and differs from it only in the double medullary shell, composed of two concentric latticed spheres; sometimes the inner medullary shell is spherical, the outer lenticular; the latter is connected with the lenticular phacoid shell (or cortical shell) by radial beams.

1. Coccodiscus lamarckii, n. sp. (Pl. 36, fig. 1).

Phacoid shell (or lenticular porous cortical shell) very thick walled (as thick as one ring), three times as broad as the outer and seven times as broad as the inner medullary shell, surrounded by two to three chambered rings of equal breadth, each of which is divided by piercing radial beams into thirty-six to forty square chambers. Margin of the disk circular, smooth. Pores regular, circular, of equal size; ten on the radius of the phacoid shell, two on the breadth of each chamber.

Dimensions.—Diameter of the disk (with two rings) 0.2, of the phacoid shell 0.14, outer medullary shell 0.05, inner 0.02.

Habitat.—Western Tropical Pacific, Station 220, depth 1100 fathoms.

2. Coccodiscus darwinii, Haeckel.

Coccodiscus darwinii, Haeckel, 1862, Monogr. d. Radiol., p. 486, Taf. xxviii. figs. 11, 12.

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by five to eight chambered rings of equal breadth, each of which is divided by forty piercing radial beams into forty square chambers of equal size. Margin of the disk smooth, circular. Pores irregular, roundish, of unequal size; eleven on the radius of the phacoid shell, one to two on each chamber.

Dimensions.—Diameter of the disk (with eight rings) 0.32, of the phacoid shell 0.11, outer medullary shell 0.036, inner 0.012.

Habitat.—Mediterranean, Messina, surface.

3. Coccodiscus goethei, n. sp. (Pl. 36, fig. 2).

Phacoid shell two and a half times as broad as the outer and five times as broad as the inner medullary shell, surrounded by three to seven chambered rings of equal breadth, each of which is divided by piercing radial beams into sixty to eighty chambers. Margin of the disk thorny. Pores regular, circular; eight on the radius of the phacoid shell, a single one on the breadth of each chamber.

Dimensions.—Diameter of the disk (with seven rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.04, inner 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subfamily 2. Stylocyclida, Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with solid radial spines on the margin of the circular disk, situated in its equatorial plane (without chambered arms).

Genus 198. Stylocyclia,^[237] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Coccodiscida with two opposite solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Stylocyclia opens the series of the Stylocyclida or of those Coccodiscida in which the margin of the chambered disk is armed with solid radial spines, situated in its equatorial plane, but without chambered arms. Stylocyclia is the most simple form of this subfamily, and bears only two marginal spines, opposite in one equatorial axis of the disk. The medullary shell is simple. This genus corresponds to Xiphodictya in the family Porodiscida. The genus was previously known only by one single species described by Ehrenberg.

1. Stylocyclia dimidiata, Ehrenberg.

Stylocyclia dimidiata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxix. fig. 4.

Phacoid shell three times as broad as the medullary shell, surrounded by five to eight chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square chambers. Pores subregular, circular; six to seven on the radius of the phacoid shell, a single one on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.)

Dimensions.—Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.11, of the medullary shell 0.035.

Habitat.—Fossil in the Tertiary rocks of Barbados; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. Stylocyclia prionacantha, n. sp. (Pl. 37, fig. 6).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. Pores in the thick-walled phacoid shell regularly circular, increasing in size from the centre; eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad serrated edges.

Dimensions.—Diameter of the disk (with five rings) 0.23, of the phacoid shell 0.12, of the medullary 0.05.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Stylocyclia excavata, n. sp. (Pl. 37, fig. 8).

Phacoid shell four times as broad as the medullary shell, surrounded by four chambered rings, which are divided by twenty to thirty radial beams into broad chambers. The height of the rings increases strongly from the centre, so that the fourth ring is two and a half times as high as the first. Pores irregular, roundish; five to six on the radius of the phacoid shell, one to two on the breadth of each ring. Margin of the disk smooth. Both marginal spines thin and long, cylindrical, arising from the medullary shell, longer than the diameter of the disk.

Dimensions.—Diameter of the disk (with four rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.025.

Habitat.—Fossil in the rocks of Barbados. Indian Ocean, Cocos Islands, Rabbe.

4. Stylocyclia amphacantha, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by five chambered rings, divided by piercing beams each into forty to fifty chambers. Pores regular, circular; eight to nine on the radius of the phacoid shell, one on each chamber. Margin of the disk thorny. Both marginal spines strong, conical, as long as its radius.

Dimensions.—Diameter of the disk (with five rings) 0.24, of the phacoid shell 0.1, of the medullary shell 0.05.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 199. Amphicyclia,^[238] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite solid radial spines on the margin of the circular disk. Medullary shell double.

The genus Amphicyclia has the same form and structure as Stylocyclia, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation that Coccodiscus does to Lithocyclia.

1. Amphicyclia chronometra, n. sp. (Pl. 38, fig. 1).

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by two broad chambered rings, which are divided into irregular chambers by fifty to sixty radial beams of different distance. Margin of the disk thorny, lacerated. Pores irregular, roundish; twelve to sixteen on the radius of the phacoid shell, two to three on the breadth of each ring. The two opposite marginal spines strong, prismatic, with prominent edges, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with two rings) 0.24, of the phacoid shell 0.15, outer medullary shell 0.05, inner 0.017.

Habitat.—Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

2. Amphicyclia amphistyla, n. sp. (Pl. 37, fig. 7).

Stylocyclia amphistyla, Haeckel, 1879, MS. et Atlas (pl. xxxvii. fig. 7).

Phacoid shell thin walled, two and a half times as broad as the outer and seven times as broad as the inner medullary shell, divided by eighty to ninety radial beams into irregular chambers, which are stratified in four to five floors. Pores regular, circular; eight to nine on the radius of the phacoid shell, two on the breadth of each chamber. Both marginal spines cylindrical.

Dimensions.—Diameter of the disk (with seven rings) 0.27, of the phacoid shell 0.1, outer medullary shell 0.04, inner 0.014.

Habitat.—North Atlantic, Canary Islands, Station 354, surface.

3. Amphicyclia pachydiscus, n. sp. (Pl. 38, fig. 2).

Phacoid shell very thick, spongy, twice as broad as the outer and five times as broad as the inner medullary shell, divided by fifty to seventy radial beams into subregular chambers, which are stratified in five to six floors. Pores irregular, roundish; ten to twelve on the radius of the phacoid shell, two to three on the breadth of each chamber. The two opposite marginal spines quadrangular prismatic, very long, as broad as the radius of the inner medullary shell. Fig. 2 exhibits a vertical section (slide) through the centre.

Dimensions.—Diameter of the disk (with five rings) 0.22, of the phacoid shell 0.1, outer medullary shell 0.05, inner 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms; fossil in Barbados.

Genus 200. Trigonocyclia,^[239] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with three solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Trigonocyclia (only known by one single species, once observed) bears on the margin of the chambered disk three solid radial spines, at equal distances one from another. It corresponds to the genus Tripodictya amongst the Porodiscida.

1. Trigonocyclia triangularis, n. sp. (Pl. 37, fig. 5).

Phacoid shell three times as broad as the medullary shell, connected with it by six equidistant radial beams, three of which are prolonged into marginal spines. In the equatorial plane only one single chambered ring, divided by forty-four radial beams into narrow chambers. Pores large, irregular, roundish; five on the radius of the phacoid shell, two on each chamber. Surface and margin of the disk spiny. Three strong conical marginal spines, divergent at equal angles, as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.16, of the phacoid shell 0.12, of the medullary shell 0.04.

Habitat.—Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

Genus 201. Staurocyclia,^[240] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with four solid radial spines on the margin of the disk, crossed in two equatorial diameters perpendicular one to another. Medullary shell simple.

The genus Staurocyclia is characterised by four radial spines on the margin of the disk, which are opposite in pairs and situated in two equatorial diameters, commonly perpendicular one to another. They form therefore a rectangular cross (rarely more or less irregular). The genus corresponds exactly to Staurodictya in the family Porodiscida. The medullary shell is simple.

1. Staurocyclia cruciata, n. sp. (Pl. 37, fig. 1).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by six to eight regular rings, which are divided by fifty to seventy piercing beams into square chambers. Pores regular, circular; six on the radius of the phacoid shell, one single pore on each chamber. Four crossed radial spines, arising from the medullary shell by thin bases, prolonged over the dentated margin as four strong quadrangular swords, as long as the radius of the disk.

Dimensions.—Diameter of the disk (with eight rings) 0.23, of the phacoid shell 0.09, of the medullary shell 0.035.

Habitat—Pacific, central area, Station 267, depth 2700 fathoms.

2. Staurocyclia serrata, n. sp.

? Haliomma sp., Bury, 1862, Polycystins of Barbados, pl. xxii. fig. 2.

Phacoid shell twice as broad as the medullary shell, surrounded by three to four spongy rings, which are divided by thirty to forty radial beams into irregular chambers. Pores in the phacoid shell regular, circular, five on its radius; in the chambered spongy girdle much smaller and irregular. Margin dentated, with four crossed, very large, quadrangular spines, as long as the radius of the disk, with wing-shaped, serrated edges.

Dimensions.—Diameter of the disk (with four rings) 0.2, of the phacoid shell 0.1, of the medullary shell 0.05.

Habitat.—Fossil in the rocks of Barbados.

3. Staurocyclia phacostaurus, n. sp. (Pl. 37, figs. 2, 3).

Phacostaurus pyramidalis, Haeckel, 1879, MS. (as a separate genus).

Phacoid shell two and a quarter times as broad as the medullary shell, connected with it by twelve radial beams (four equatorial and eight divergent) and surrounded by one single ring, which is divided by forty radial beams into regular chambers. Pores regular, honeycomb-like in the phacoid shell, seven on its radius; smaller on the equatorial ring, three on its breadth. Four marginal spines pyramidal four-sided, as long and as broad at the base as the ring.

Dimensions.—Diameter of the disk (with one ring) 0.14, of the phacoid shell 0.11, of the medullary shell 0.048.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

4. Staurocyclia magniducis, n. sp. (Pl. 37, fig. 4).

Coccostaurus magniducis, Haeckel, 1881, MS. et Atlas (pl. xxxvii. fig. 4).

Phacoid shell twice as broad as the medullary shell, connected with it by numerous radial beams and surrounded by eight chambered rings, which are divided by one hundred to one hundred and twenty piercing radial beams into small chambers. Pores subregular, circular; ten on the radius of the phacoid shell, two on the breadth of each chamber. Margin of the disk armed with numerous bristle-shaped radial spines, as long as the breadth of the chambered girdle. Four very large crossed spines, nearly as long as the diameter of the disk, quadrangular, with four dentated edges; at the club-shaped distal end thorny, as broad as the medullary shell and three times as broad as at the narrow base. I name this splendid species in the honour of H.R.H. the Grand Duke of Saxe-Weimar, Carl Alexander, the magnanimous protector of arts and sciences, the rector magnificentissimus of the University of Jena.

Dimensions.—Diameter of the disk (with eight rings) 0.27, of the phacoid shell 0.11, of the medullary shell 0.05; length of the four crossed club-spines 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—Indian Ocean, Ceylon, Belligemma, surface (Haeckel).

Genus 202. Astrocyclia,^[241] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with numerous (five or more, commonly thirty to sixty) solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Astrocyclia exhibits on the margin of the circular chambered disk a large but variable number of solid radial spines, commonly between thirty and sixty. They are the external prolongations of the inner piercing radial beams, which divide the concentric rings of the disk into chambers. All the spines lie in the equatorial plane of the disk. The genus corresponds to Stylodictya in the family Porodiscida.

1. Astrocyclia solaster, n. sp. (Pl. 36, fig. 7).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by four to six regular rings of equal breadth, which are divided by thirty to forty piercing radial beams into broad chambers. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber (the size increasing from the centre). Margin with thirty to forty angular, broad, dentate spines, the prolongations of the inner radial beams.

Dimensions.—Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.04.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Astrocyclia stella, Haeckel.

Lithocyclia stella, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. xxix. fig. 2.

Phacoid shell three times as broad as the medullary shell, surrounded by four to eight rings of increasing breadth from the centre, the outer of which are more or less spongy. Each ring is divided by forty to fifty piercing radial beams into chambers of increasing size. Pores regular, circular; a single one on each chamber, ten on the radius of the phacoid shell. On the margin are scattered ten to twenty thick and short spines, four-sided pyramidal, about as long and as broad at the base as the diameter of the medullary shell.

Dimensions.—Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.09, of the medullary shell 0.03.

Habitat.—Fossil in the rocks of Barbados.

3. Astrocyclia rotula, n. sp.

Phacoid shell four times as broad as the medullary shell, surrounded by one single ring, which is divided by forty radial beams into equal chambers. Pores regular, circular; two on the breadth of the ring, six on the radius of the phacoid shell. Margin with forty short, conical spines, the prolongations of the inner radial beams, twice as long as the breadth of the ring.

Dimensions.—Diameter of the disk 0.13, of the phacoid shell 0.1, of the medullary shell 0.025.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

4. Astrocyclia arachnia, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by four to six rings of equal breadth, which are divided by twelve to twenty radial beams into broad chambers. Pores regular, circular; two on the breadth of each ring, eight on the radius of the phacoid shell. Margin with twelve to twenty very long and thin, bristle-shaped, radial spines, the prolongations of the inner beams, longer than the diameter of the disk. (Resembles Stylodictya arachnia, but differs in the possession of a phacoid shell.)

Dimensions.—Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.09, of the medullary shell 0.045.

Habitat.—North Atlantic, Canary Islands.

5. Astrocyclia heterocycla, n. sp. (Pl. 36, fig. 8). Phacoid shell two and a half times as broad as the medullary shell, surrounded by three rings of unequal breadth, the first ring as broad as the second and third together. They are divided by fifty to sixty piercing radial beams into chambers, which are square in the second and third rings, and half as large as in the first. The radial beams are alternately thicker and thinner, prolonged into short marginal spines. Pores subregular, circular; eight on the radius of the phacoid shell, two on the breadth of the first ring, a single one on each chamber of the second and third rings.

Dimensions.—Diameter of the disk (with three rings) 0.2, of the phacoid shell 0.12, of the medullary shell 0.05.

Habitat.—Equatorial Atlantic, Station 348, depth (2450) fathoms; also fossil in Barbados.

Genus 203. Coccocyclia,^[242] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with numerous (five or more) solid radial spines on the margin of the circular disk. Medullary shell double.

The genus Coccocyclia has the same form and structure as the foregoing Astrocyclia, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation as Coccodiscus to Lithocyclia.

1. Coccocyclia liriantha, n. sp.

Phacoid shell three times as broad as the outer and ten times as broad as the inner medullary shell, connected with both by six equidistant piercing radial beams. The margin of the phacoid shell is surrounded by one or two equatorial rings, each as broad as the outer medullary shell, and divided by thirty to forty radial beams into narrow chambers. Pores subregular, circular, about nine to ten on the radius of the phacoid shell, three to four on the breadth of each ring. Margin of the disk ciliated, with six regularly disposed radial spines as prolongations of the inner six piercing beams. Each spine cylindrical, delicately crenulated, about as broad as the inner medullary shell, and once to twice as long as the diameter of the whole disk, elegantly undulated, with a conical terminal point.

Dimensions.—Diameter of the disk (with two rings) 0.32, of the phacoid shell 0.2, of the outer medullary shell 0.06, of the inner 0.02.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

2. Coccocyclia heliantha, n. sp. (Pl. 36, figs. 5, 6).

Phacoid shell two and a half times as broad as the outer and six times as broad as the inner medullary shell, surrounded by six to eight rings of nearly equal breadth, the outer somewhat smaller. They are divided by fifty to sixty piercing radial beams into irregular chambers. Pores irregular, roundish; ten on the radius of the phacoid shell, a single one on each chamber of the equatorial girdle. Margin of the disk with numerous strong conical radial spines of different breadths, arranged in several circles, the strongest in the equatorial plane, about as broad as one ring and twice as long. Surface thorny.

Dimensions.—Diameter of the disk (with seven rings) 0.3, of the phacoid shell 0.12, of the outer medullary shell 0.05, of the inner 0.02.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subfamily 3. Astracturida, Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two or more (commonly three or four) chambered radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 204. Diplactura,^[243] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite chambered arms on the margin of the circular disk, without a connecting patagium.

The genus Diplactura is the simplest form of the Astracturida, or of those Coccodiscida in which the margin of the disk bears chambered arms, situated in its equatorial plane. This subfamily corresponds to the Euchitonida among the Porodiscida, to the Spongobrachida among the Spongodiscida. In Diplactura there are only two free arms, opposite in one equatorial diameter (corresponding to Amphibrachium among the former, to Spongolena among the latter).

Subgenus 1. Diplacturium, Haeckel.

Definition.—Arms blunt at the distal end, without radial spines.

1. Diplactura diplobrachia, n. sp.

Phacoid shell twice as broad as the medullary shell, with six pores on its radius, without a perfect chambered ring around it. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, at the distal end rounded, blunt, as broad as the latter, at the base only half as broad.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.12, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Diplactinium, Haeckel.

Definition.—Arms on the distal end armed with a radial terminal spine.

2. Diplactura diploconus, n. sp. (Pl. 38, fig. 5).

Amphiactura diploconus, Haeckel, 1877, MS. et Atlas (pl. xxxviii. fig. 5).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by a single chambered ring. Arms club-shaped, twice as long as the diameter of the phacoid shell, at the distal end as broad as the latter, at the base only half as broad. Both poles of the common axis of the arms are armed with a strong spindle-shaped terminal spine.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms (without terminal spines) 0.17, basal breadth 0.05, distal breadth 0.09.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Genus 205. Amphiactura,^[244] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite chambered arms on the margin of the circular disk, connected by a spongy patagium.

The genus Amphiactura differs from the foregoing Diplactura in the development of a patagium between the arms, and therefore bears the same relation to it as Amphymenium in the Porodiscida does to Amphibrachium, or Spongobrachium in the Spongodiscida does to Spongolene. In this and in the following Discoidea provided with a patagium, this connecting web constantly exhibits a different texture of its framework, which is sometimes more regularly chambered, at other times more irregularly spongy.

1. Amphiactura amphibrachia, n. sp. (Pl. 38, figs. 3, 4).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as the latter, at the base only one-third as broad. Patagium a circular lenticular disk, enveloping only the basal third of the arms, with three to four concentric circular rings, divided into chambers by about forty radial beams, which are prolonged beyond the margin of the patagium into radial spines. The vertical section (fig. 4) shows that the chambers of each arm (eleven to twelve transverse rows in the radius) are disposed in two layers.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.18, basal breadth 0.03, distal breadth 0.09.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Genus 206. Trigonactura,^[245] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with three chambered arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus Trigonactura exhibits three radial arms, which in all known species are separated by three equal angles. The terminal points of the arm-axes are the corners of an equilateral triangle. It corresponds therefore to Dictyastrum among the Porodiscida.

Subgenus 1. Trigonacturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without a terminal spine.

1. Trigonactura pythagoræ, Haeckel.

Astromma pythagoræ, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 2.

Phacoid shell circular, twice as broad as the medullary shell, with five pores on its radius, without a completely surrounding chambered girdle. Arms nearly square, at the truncated distal end as broad as long, and scarcely broader than at the base, two-thirds as long as the diameter of the central disk.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.07, distal breadth 0.07.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, in various depths; also fossil in Tertiary rocks of Barbados and Nicobar.

2. Trigonactura rhopalastrella, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 7.

Phacoid shell twice as broad as the medullary shell, with five pores on its radius, without a perfect chambered ring around it. Arms club-shaped, at the blunt distal end rounded, as long as the diameter of the phacoid shell; their basal breadth is one-fourth, their distal breadth one-half of its length.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.1, basal breadth 0.025, distal breadth 0.05.

Habitat.—Pacific, central area, Stations 270 to 274, depths 2400 to 2800 fathoms; also fossil in Tertiary rocks of Barbados.

3. Trigonactura trigonobrachia, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with six pores on its radius, without a perfect chambered girdle. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as its diameter and three times as broad as at the narrow base. (Resembles Hymenactura hexagona, but without a patagium.)

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.045; length of the arms 0.2, basal breadth 0.035, distal breadth 0.1.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Trigonactura lanceolata, n. sp.

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms lanceolate, three times as long as the diameter of the phacoid shell, and four times as long as broad in the middle part, at both ends very narrow, blunt.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.25, breadth in the midst 0.06.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. Trigonactinium, Haeckel.

Definition.—Distal end of the arms armed with a radial spine.

5. Trigonactura triacantha, n. sp. (Pl. 38, figs. 6, 7).

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end with a strong pyramidal terminal spine. Through the spongy framework of each arm shine sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing beams.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.038; length of the arms 0.2, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

6. Trigonactura trigonodiscus, n. sp.

? Astromma sp., Bury, 1862, Polycystins of Barbados, Taf. xv. fig. 2.

Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven pores on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as the diameter of the central disk and at the base half as broad, slowly decreasing in breadth towards the distal end, which is armed with a strong pyramidal spine.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, basal breadth 0.07.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

7. Trigonactura trixiphos, n. sp.

Phacoid shell circular, twice as broad as the medullary shell, without a completely surrounding chambered ring, with four pores on its radius. Arms club-shaped, about as long as the diameter of the central disk, at the base half as broad as long, at the rounded distal end broader, and armed with a strong pyramidal terminal spine, nearly as long as the arm itself.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms (without terminal spine) 0.08, basal breadth 0.04, distal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados.

Genus 207. Hymenactura,^[246] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with three chambered arms on the margin of the circular or triangular disk, connected by a spongy patagium.

The genus Hymenactura differs from the foregoing Trigonactura in the spongy patagium between the arms, and bears therefore to it the same relation that among the Porodiscida Hymeniastrum does to the simpler Dictyastrum. The oldest known species of this genus is Hymenactura pythagoræ, described by Ehrenberg as Hymeniastrum pythagoræ, but differing from this in the structure of the central disk.

Subgenus 1. Hymenacturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Hymenactura archimedis, n. sp. (Pl. 38, fig. 8).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base only half as broad. In each arm eleven to twelve transverse rows of square chambers, each of which exhibits on the surface one large pore. Patagium enveloping the basal half of the arms, with four to five convex rows of chambers, forming together a circular concentric disk.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.035; length of the arms 0.12, basal breadth 0.05, distal breadth 0.1.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Hymenactura pythagoræ, Haeckel.

Hymeniastrum pythagoræ, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 31; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 76, Taf. xxx. fig. 5.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base two-thirds as broad. In each arm eight to nine transverse rows of square chambers, each chamber with one pore on the surface. Patagium enveloping the basal half of the arms, with four to five rectilinear parallel rows of chambers, forming together a regular triangle. Differs from the preceding species mainly in the quite different structure of the patagium, from the true Hymeniastrum pythagoræ in the phacoid shell of the central disk, which encloses only one simple medullary shell.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.13, basal breadth 0.07, distal breadth 0.12.

Habitat.—Fossil in the rocks of Barbados.

3. Hymenactura trigona, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 1.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms slender, lanceolate, three times as long as the diameter of the phacoid shell and five times as long as broad in the middle part; distal ends blunt. Patagium enveloping only the basal half of the arms, forming a regular triangle with concave sides.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.035; length of the arms 0.2, greatest breadth 0.04.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms; fossil in the rocks of Barbados.

4. Hymenactura hexagona.

Hymeniastrum sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 3.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms nearly equilateral triangular, three times as long as the diameter of the phacoid shell, at the truncated distal end nearly three-fourths as broad as long, at the narrow base only one-fourth as broad. Patagium complete, enveloping the arms completely, so that the whole body represents a regular hexagonal disk.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.18, basal breadth 0.04, distal breadth 0.16.

Habitat.—Fossil in the rocks of Barbados and Nicobar.

Subgenus 2. Hymenactinium, Haeckel.

Definition.—Distal ends of the arms armed with terminal spines.

5. Hymenactura ptolemæi, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xv. figs. 5, 6.

Phacoid shell twice as broad as the medullary shell, with six to seven pores on its radius. Arms nearly square, about as large as the phacoid shell, at the truncated distal end little broader than at the base, and armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping the basal half of the arms.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length and greatest breadth of the arms 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; fossil in the rocks of Barbados.

6. Hymenactura copernici, n. sp. (Pl. 38, fig. 9).

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms lanceolate, nearly twice as long as the phacoid shell, in the middle part twice as broad as the medullary shell, with a strong conical terminal spine at the distal end. In each arm about ten transverse rows of chambers. Patagium enveloping the basal half of the arms, with four convex parallel rows of chambers.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.17, greatest breadth 0.07.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Genus 208. Astractura,^[247] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, without a connecting patagium.

The genus Astractura has the form of a regular cross, four radial arms being opposite in two equatorial diameters perpendicular one to another. In the Porodiscida the same form is repeated by Stauralastrum, in the Spongodiscida by Spongasteriscus. The oldest known species of the genus is Astromma aristotelis of Ehrenberg, in which genus this author confounded triradial and four-radial forms.

Subgenus 1. Astracturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Astractura ordinata, n. sp.

? Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 3.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius, without a completely developed chambered ring. Arms trapezoidal, somewhat longer than the radius of the disk, at the truncated distal end as broad as long, at the base one-third smaller.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.03; length of the arms 0.05, distal breadth 0.05, basal breadth 0.035.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

2. Astractura clavigera, n. sp.

Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pl. iv. fig. 2.

Phacoid shell twice as broad as the medullary shell, with ten pores on its radius, surrounded by one perfect chambered ring. Arms club-shaped, about as long as the radius of the central disk, at the rounded distal end two-thirds, at the base one-third as broad as long.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.06, basal breadth 0.02, distal breadth 0.04.

Habitat.—Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms; fossil in the rocks of Barbados.

Subgenus 2. Astractinium, Haeckel.

Definition.—Distal end of the arms furnished with a radial spine.

3. Astractura aristotelis, Haeckel.

Astromma aristotelis, Ehrenberg, 1856, Microgeol., Taf. xxxvi. fig. 32; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 66, Taf. xxx. fig. 4.

Astromma aristotelis, Haeckel, 1862, Monogr. d. Radiol., p. 489.

? Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell three times as broad as the medullary shell, with six to eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly trapezoidal, about as long as the diameter of the central disk, at the base half as broad, at the truncated distal end nearly as broad as long, and armed with a large pyramidal terminal spine. Each arm with about eight transverse and longitudinal rows of chambers.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.1, basal breadth 0.05, distal breadth 0.09.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, at various depths; fossil in the Tertiary rocks of Barbados and Nicobar.

4. Astractura democriti, n. sp.

Astromma aristotelis, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf, xxx. fig. 3.

? Astromma aristotelis, var., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell twice as broad as the medullary shell, with five to seven pores on its radius, without perfect chambered ring. Arms about twice as long as broad, longer than the diameter of the central disk, at the truncated distal end a little broader than at the base, and armed with a strong, pyramidal, terminal spine.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.15, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms; fossil in Barbados.

5. Astractura hippocratis, n. sp.

Phacoid shell three times as broad as the medullary shell, with seven pores on its radius, surrounded by two to three perfect chambered rings. Arms nearly square, scarcely as long and nearly as broad as the diameter of the central disk, at the rounded distal end armed with a very strong, pyramidal, terminal spine, longer than the arm itself, and at the base as broad as the medullary shell.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.08, breadth 0.1.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 209. Stauractura,^[248] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, connected by a spongy patagium.

The genus Stauractura differs from the foregoing in the patagium between the arms, and bears therefore the same relation to it as Histiastrum in the Porodiscida does to Stauralastrum. All known species of this genus form a regular square, if we connect the end points of the arm axes by lines.

Subgenus 1. Stauracturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Stauractura octogona, n. sp.

Phacoid shell twice as broad as the medullary shell, with eight pores in its radius. Arms nearly square, little larger than the phacoid shell, with broad truncated distal ends. The corners of the latter are so connected by the complete patagium, that the whole shell forms a regular octagon.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, distal breadth 0.11.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Stauractura tetragona, n. sp.

Phacoid shell three times as broad as the medullary shell, with eleven pores on its radius. Arms club-shaped, nearly as long as the diameter of the phacoid shell, and one and a half times as long as broad at the distal part; at the distal end rounded, blunt, without terminal spine. The terminal points of the arms are so connected by a thin, complete patagium, that the whole shell becomes a regular square.

Dimensions.—Diameter of the phacoid shell 0.13, of the medullary shell 0.045; length of the arms 0.12, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Stauractinium, Haeckel.

Definition.—Distal end of the arms furnished with a radial spine.

3. Stauractura medusina, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, and in the outer third nearly as broad as the latter, at the base scarcely one-third as broad; their truncated distal end armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping only the basal half of the arms, with three rectilinear parallel rows of chambers, forming a square.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length of the arms 0.14, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

4. Stauractura quadrata, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on the radius. Arms nearly square, about as large as the phacoid shell, with a strong pyramidal terminal spine at the distal end. Patagium complete, between every two arms triangular, with rectilinear parallel rows of chambers; it connects the end points of the arm radius in such a manner that the whole shell becomes a regular square.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.1, greatest breadth 0.08.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Genus 210. Pentactura,^[249] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with five chambered arms on the margin of the circular or pentagonal disk, without a connecting patagium.

The genus Pentactura possesses five free radial arms, and resembles Pentalastrum among the Porodiscida. The distance of the five arms seems to be sometimes equal, at other times different in one and the same species.

1. Pentactura pentactis, Haeckel.

Astromma pentactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 1.

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius. Arms regularly or irregularly disposed, nearly square, about half as large as the phacoid shell, at the truncated distal end little broader than at the base. In the specimen figured, and very imperfectly described by Ehrenberg, (loc. cit.), the arms were asymmetrically disposed, two opposite in one axis of the disk, two others on one side of this axis, the fifth opposite to these on the other side. Another specimen which I found in the Barbados rocks had five arms of equal size, regularly disposed, at equal intervals.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length and breadth of the arms 0.05 to 0.06.

Habitat.—Fossil in the rocks of Barbados.

2. Pentactura astropecten, n. sp.

Phacoid shell three times as broad as the medullary shell, with ten pores on its radius. Arms regularly disposed, club-shaped, nearly twice as long as the diameter of the phacoid shell, and equal to it in breadth at the rounded distal end. The latter is armed with a short conical spine, and is twice as broad as the base.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.17, basal breadth 0.05, distal breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 211. Echinactura,^[250] n. gen.

Definition.—Coccodiscida with five chambered arms on the margin of the circular or pentagonal disk, connected by a spongy patagium.

The genus Echinactura differs from the foregoing Pentactura in the patagium between the arms, and bears therefore the same relation to it as Pentinastrum in the Porodiscida does to Pentalastrum.

1. Echinactura culcita, n. sp.

Phacoid shell pentagonal, three times as broad as the medullary shell, with nine pores on its radius. Arms egg-shaped, about as long as the diameter of the phacoid shell, and in the distal part half as broad. The blunt ends of the arms are so connected by the complete patagium that the whole shell becomes a regular pentagonal disk.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.11, basal breadth 0.04, distal breadth 0.06.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Echinactura asteriscus, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on its radius. Arms lanceolate, twice as long as the diameter of the phacoid shell, in the middle part nearly as broad as the latter, at the distal end with a strong conical terminal spine. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.2, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Echinactura goniaster, n. sp.

Phacoid shell three times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, in the distal part nearly as broad as the latter, in the basal part one-third as broad; at the end a strong pyramidal spine. Patagium nearly complete, with concave dentated margin between each pair of arms, therefore the pentagonal disk of the whole shell with concave sides.

Dimensions.—Diameter of the phacoid shell 0.12, of the medullary shell 0.04; length of the arms (without terminal spine) 0.18, basal breadth 0.04, distal breadth 0.1.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Family XXI. Porodiscida, Haeckel (Pls. 41-47).

Definition.—Discoidea without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by concentric chambered rings (each ring divided by radial beams into imperfect chambers). Surface of the disk on the two flat sides covered by a porous sieve-plate.

The family Porodiscida is by far the largest and richest in different and common forms among all Discoidea; already in my Monograph (1862) nine genera and twenty-eight species have been enumerated. Their number is here increased to more than thirty genera and two hundred species. Many of these species appertain to the most common and widely distributed Spumellaria, both living and fossil. But the study of their structure is not easy, and requires (as in the foregoing Coccodiscida) not only careful examination of the facial views of the disk, but also of the marginal view and of slides and sections through different planes.

In my Monograph (1862, pp. 485, 491, 513) I had constituted for these Discoidea two different families, the Trematodiscida and Discospirida; but the comparative study of a far greater number of different types in the Challenger collection has since convinced me that those two families are but little different, and united by transitional forms within one and the same genus, so that they must be united as Porodiscida. Of the group, which Ehrenberg formerly had called "Calodictya," many genera appertain to the Porodiscida, whilst many others are true Spongodiscida.

The Porodiscida represent the first and the most important family of the Cyclodiscaria, or of those Discoidea which are devoid of the peculiar extracapsular lenticular "phacoid shell," characteristic of the three preceding families (united therefore as Phacodiscaria). Probably all Cyclodiscaria can be derived from Archidiscus, from a morphological as well as a phylogenetic point of view. Archidiscus seems to be the common ancestral form not only of the Porodiscida, but also of the nearly allied Pylodiscida and Spongodiscida. This important Archidiscus (Pl. 48, figs. 9-11) is a small lenticular circular disk, in which a simple latticed spherical central chamber is surrounded by one single concentric ring, connected with it by a variable number of radial beams in the equatorial plane. From this typical Archidiscus, as from their "architype," all other Cyclodiscaria may be derived; the Porodiscida by regular apposition of new concentric chambered rings on the margin, the Spongodiscida by irregular apposition of a spongy framework, the Pylodiscida by a peculiar interrupted, concentric, triradial growth, three radial arm-chambers alternating with three open gates or holes, so that already the first chambered ring is not complete.

Archidiscus (Pl. 48, figs. 9-11) is not only the common phylogenetic ancestral form of all Cyclodiscaria, but also the common ontogenetic original form of all Porodiscida, or at least of the greater part of them. The numerous species of Archidiscus, which are distinguished in the sequel, are at the same time the embryonic forms of different Porodiscida, corresponding to the "biogenetic main law of development." The small shell of Archidiscus is sometimes completely lenticular, circular, at other times more or less polygonal; commonly on the biconvex centre much thicker than on the margin, but sometimes also of nearly equal thickness (like a medal or a short cylinder). The latticed central chamber of it is probably in the majority of species spherical, but in some more or less compressed, lenticular; the number of small pores on its surface is probably commonly between ten and twenty (four to eight usually being visible on each hemisphere). The number of radial beams, which connect it with the equatorial ring, varies commonly from four to eight; but sometimes only two or three are to be found, in other cases nine to ten or more. The regular disposition of these beams (in certain equatorial axes of the disk) is probably of great importance, as determining the later development of characteristic radial appendages of the margin in the more highly developed Porodiscida. The equatorial ring itself, forming the margin of the lenticular disk, is either a simple solid ring or a broader latticed girdle; in the latter case it merges slowly into the opposite sieve-plates of the two flat disk sides, or the porous "cover-plates," covering its parallel or convex surfaces. These latter can be regarded as direct peripheral continuations of the polar regions of the spherical central chamber. The ring-chambers, surrounding the latter in a single circle, are commonly of nearly the same breadth, but often also of different irregular size. Their number varies between two and ten or more, but commonly between four and eight; each ring-chamber is covered on the upper and lower side by the sieve-plate, bounded on the inner (proximal) side by the wall of the central chamber, on the outer (distal) side by the marginal ring, on both lateral sides by the contiguous neighbouring ring-chambers.

The important question as to the phylogenetic origin of Archidiscus can be answered in a twofold way. The most simple form of Archidiscus (Archidiscus dioniscus) can be derived immediately from the Stylosphærida, Saturnalis (Pl. 13, fig. 16), only by the development of lattice-work between the equatorial ring and the two polar faces of the concentric central chamber (on the surface of the biconvex jelly-mantle). But on the other hand Archidiscus may also be derived from the simplest Phacodiscida, Sethodiscus (Pl. 33, figs. 1-3), by the stronger compression of the biconvex lenticular shell, so that the enclosed medullary shell on the two poles runs together with the lenticular phacoid shell, of which only the peripheral part remains free, and thus forms the chambered ring; this latter explanation seems the more natural in many cases, as often in the Porodiscida the central chamber is enclosed in one or two concentric spherical or lenticular lattice-shells.

The second subfamily of the Porodiscida are the Trematodiscida, which are derived from the preceding Archidiscida by concentric growth in the equatorial plane. In the same way in which the simple chambered ring of Archidiscus is connected by radial beams with the central chamber, so in Porodiscus a variable number of concentric rings is connected with that first ring. The number of these concentric rings varies between two and ten or more, but commonly amounts to between three and five. The radial beams connecting them are either piercing or interrupted; their number increases gradually from the centre towards the periphery. The chambers between them are sometimes more regular, at other times more irregular in size and form. Their upper and lower wall is formed by the two covering "sieve-plates," or the porous cover-plates, which are continued from the central disk to the margin. If these two sieve-plates continue being parallel, the disk becomes medal-shaped or a short cylinder; if the two plates become more or less concavely vaulted one against the other, the disk becomes biconvex lenticular, the middle part thicker than the marginal part. Rarely the contrary is the case, the margin thicker than the centre, and then the disk biconcave.

In my Monograph I had separated as two different subfamilies the true Trematodiscida (with circular concentric rings) from the Discospirida (with spirally convoluted rings). But the enormous mass of specimens, which I afterwards examined in the Challenger collection, has convinced me that this separation was not natural. For in one and the same genus of most nearly allied forms we find on one hand quite regular concentric circular forms (Trematodiscus), on the other hand spirally convoluted forms (Discospira), and connecting between them such forms as are in the central part concentric, in the marginal part spiral (Perispira)—or conversely, these in the centre spiral, on the margin concentric (Centrospira)—and frequently also more or less irregular forms with interrupted rings (Atactodiscus); therefore, all those genera (Prodromus, 1881, Nos. 448-452) have only the value of subgenera of Porodiscus. But a distinct genus is Perichlamydium, in which the two sieve-plates run on the margin of the lens and form a broad hyaline porous or solid girdle. More important is the distinction of the Ommatodiscida, in which the margin of the disk exhibits one larger osculum, armed with a corona of spines (Ommatodiscus), or two oscula, opposite on the poles of one axis (Stomatodiscus). Whilst in many Porodiscida all chambers of the concentric rings lie in one and the same (equatorial) plane, in many others with further growth they become stratified in floors, and the whole disk is therefore composed of two to four or more parallel disks, each with a system of concentric chambered rings or girdles, quite as in the majority of the Coccodiscida (p. 457). Often the central part of the lenticular disk becomes thickened by apposition of such floors or strata, whilst the marginal part remains simple, with one single stratum. The communication between the chambers of the different strata seems to be the same as in the similar Coccodiscida.

Also the margin of the disk exhibits in the Porodiscida the same characteristic differences as in the foregoing family. In the subfamily of Stylodictyida it bears a certain number of solid radial spines, often regularly disposed (as in the Stylocyclida). In the subfamily of Euchitonida the margin is distinguished by the possession of two to six or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure (sometimes more or less irregular, spongy). These arms are very variable in size, form, and structure, exhibit the same peculiarities as in the Astracturida, and are sometimes free, at other times connected by a "patagium" or an interbrachial spongy skeleton of different structure, like a web membrane (compare above, p. 458). In some genera the arms become forked or branched on the distal end. Sometimes their distal end bears a terminal radial spine.

The Central Capsule of the Porodiscida assumes generally the form of the including shell, with or without arms, but is constantly somewhat smaller, as it remains enclosed by the sieve-plates of the disk surface. Often the capsule is filled with many coloured oil-globules, disposed regularly in the chamber rows. The nucleus of it is enclosed by the central chamber, and in many cases by this and the innermost concentric rings.

Synopsis of the Genera of the Porodiscida.

I. Section of the Porodiscida—Archidiscaria. Central chamber of the disk surrounded only by one single chambered ring.

1. Subfamily Archidiscida. Only one single chambered girdle surrounds the central chamber; margin smooth or spiny. Margin smooth, without spines, 212. Archidiscus.

Margin armed with radial spines, 213. Axodiscus.

II. Section of the Porodiscida—Astrodiscaria. Central chamber of the disk surrounded by two or more (commonly three to six) concentric chambered rings or radiated girdles.

2. Subfamily Trematodiscida. Margin of the disk quite simple, without radial appendages (spines or chambered arms), without peculiar oscula. Margin simple, without an equatorial girdle, 214. Porodiscus.

Margin with a thin porous equatorial girdle, 215. Perichlamydium.

3. Subfamily Ommatodiscida. Margin of the disk without chambered arms but distinguished by one or two large oscula, or wide openings armed with a crown of spines. Disk with a single marginal osculum, 216. Ommatodiscus.

Disk with two opposite marginal oscula, 217. Stomatodiscus.

4. Subfamily Stylodictyida. Margin of the disk without peculiar oscular openings and without chambered arms, but armed with solid radial spines. Radial spines of the margin two, three, or four, usually quite regularly disposed. Two opposite spines, 218. Xiphodictya.

Three equidistant spines, 219. Tripodictya.

Four crossed spines, 220. Staurodictya.

Radial spines of the margin five or more, commonly irregularly disposed (generally ten to twelve). Margin simple, without an equatorial girdle, 221. Stylodictya.

Margin with a thin porous equatorial girdle, 222. Stylochlamydium.

5. Subfamily Euchitonida. Margin of the disk with radial chambered arms (or hollow chambered appendages), on the distal end of the arms with or without solid radial spines. Two arms, opposite in one main axis. Two arms simple, undivided. Without a patagium, 223. Amphibrachium.

With a patagium, 224. Amphymenium.

Two arms forked (or one simple, other forked). Without a patagium, 225. Amphirrhopalum.

With a patagium, 226. Amphicraspedum.

Three arms (either regular, equal, or bilateral, with unequal arms). Three arms simple, undivided. Without a patagium. Regular, 227. Dictyastrum.

Bilateral, 228. Rhopalastrum.

With a patagium. Regular, 229. Hymeniastrum.

Bilateral, 230. Euchitonia.

Three arms forked. Either regular or bilateral. Without a patagium, 231. Chitonastrum.

With a patagium, 232. Trigonastrum.

Four arms (either regular, with four equal crossed arms, or bilateral, with paired arms). Four arms simple, undivided. Without a patagium. Regular, 233. Stauralastrum.

Bilateral, 234. Hagiastrum.

With a patagium. Regular, 235. Histiastrum.

Bilateral, 236. Tessarastrum.

With a terminal patagial girdle, 237. Stephanastrum

Four arms forked. Without a patagium. Regular, 238. Dicranastrum.

Bilateral, 239. Myelastrum.

Five arms (equal or unequal). Five arms simple, undivided. Without a patagium, 240. Pentalastrum.

With a patagium, 241. Pentinastrum.

Five arms forked. Without a patagium, 242. Pentophiastrum.

Six arms (equal or unequal). Six arms simple, undivided. Without a patagium, 243. Hexalastrum.

With a patagium, 244. Hexinastrum.

I. Section of the Porodiscida—Archidiscaria. Central chamber of the disk surrounded only by one single chambered ring.

1. Subfamily Archidiscida. Only one single chambered girdle surrounds the central chamber; margin smooth or spiny.

Margin smooth, without spines,

212. Archidiscus.

Margin armed with radial spines,

213. Axodiscus.

II. Section of the Porodiscida—Astrodiscaria. Central chamber of the disk surrounded by two or more (commonly three to six) concentric chambered rings or radiated girdles.

2. Subfamily Trematodiscida. Margin of the disk quite simple, without radial appendages (spines or chambered arms), without peculiar oscula.

Margin simple, without an equatorial girdle,

214. Porodiscus.

Margin with a thin porous equatorial girdle,

215. Perichlamydium.

3. Subfamily Ommatodiscida. Margin of the disk without chambered arms but distinguished by one or two large oscula, or wide openings armed with a crown of spines.

Disk with a single marginal osculum,

216. Ommatodiscus.

Disk with two opposite marginal oscula,

217. Stomatodiscus.

4. Subfamily Stylodictyida. Margin of the disk without peculiar oscular openings and without chambered arms, but armed with solid radial spines.

Radial spines of the margin two, three, or four, usually quite regularly disposed.

Two opposite spines,

218. Xiphodictya.

Three equidistant spines,

219. Tripodictya.

Four crossed spines,

220. Staurodictya.

Radial spines of the margin five or more, commonly irregularly disposed (generally ten to twelve).

Margin simple, without an equatorial girdle,

221. Stylodictya.

Margin with a thin porous equatorial girdle,

222. Stylochlamydium.

5. Subfamily Euchitonida. Margin of the disk with radial chambered arms (or hollow chambered appendages), on the distal end of the arms with or without solid radial spines.

Two arms, opposite in one main axis.

Two arms simple, undivided.

Without a patagium,

223. Amphibrachium.

With a patagium,

224. Amphymenium.

Two arms forked (or one simple, other forked).

Without a patagium,

225. Amphirrhopalum.

With a patagium,

226. Amphicraspedum.

Three arms (either regular, equal, or bilateral, with unequal arms).

Three arms simple, undivided.

Without a patagium.

Regular,

227. Dictyastrum.

Bilateral,

228. Rhopalastrum.

With a patagium.

Regular,

229. Hymeniastrum.

Bilateral,

230. Euchitonia.

Three arms forked.

Either regular or bilateral.

Without a patagium,

231. Chitonastrum.

With a patagium,

232. Trigonastrum.

Four arms (either regular, with four equal crossed arms, or bilateral, with paired arms).

Four arms simple, undivided.

Without a patagium.

Regular,

233. Stauralastrum.

Bilateral,

234. Hagiastrum.

With a patagium.

Regular,

235. Histiastrum.

Bilateral,

236. Tessarastrum.

With a terminal patagial girdle,

237. Stephanastrum

Four arms forked.

Without a patagium.

Regular,

238. Dicranastrum.

Bilateral,

239. Myelastrum.

Five arms (equal or unequal).

Five arms simple, undivided. simple,

Without a patagium,

240. Pentalastrum.

With a patagium,

241. Pentinastrum.

Five arms forked.

Without a patagium,

242. Pentophiastrum.

Six arms (equal or unequal).

Six arms simple, undivided.

Without a patagium,

243. Hexalastrum.

With a patagium,

244. Hexinastrum.

Subfamily 1. Archidiscida, Haeckel.

Definition.—Porodiscida with a simple spherical or lenticular latticed central chamber, surrounded by a single concentric latticed ring, which is divided by radial beams into two to six or more radial chambers.

Genus 212. Archidiscus,^[251] n. gen.

Definition.—Porodiscida with a simple central chamber, surrounded by a single concentric ring, which is divided by radial beams into two to six or more radial chambers, without radial spines on the margin.

The genus Archidiscus begins the long and polymorphous series of the Cyclodiscaria or of those Discoidea which do not possess the peculiar "phacoid shell" characteristic of the three preceding families, united as "Phacodiscaria." As already mentioned above, both these groups are probably of independent origin, derived from the Sphæroidea in different ways (compare pp. 402, 405, &c.). Among all Cyclodiscaria Archidiscus is the most simple, and probably the common ancestral form, from which the other genera may be derived.

Subgenus 1. Dioniscus, Haeckel.

Definition.—Ring with two chambers, separated by two radial beams.

1. Archidiscus dioniscus, n. sp.

Ring circular, connected with the central chamber by two radial beams, opposite in one axis, therefore two equal semicircular ring chambers. (This primitive form has an interesting reference to Saturnalis, Pl. 13, fig. 16, and differs from it only in the lattice-work covering both faces of the lenticular disk, the margin of which forms the ring.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Archidiscus dithalamus, n. sp.

Ring roundish, connected with the central chamber by two radial beams, not opposite in one axis; both semicircular ring chambers more or less unequal, one of them larger than the other, and sometimes much more prominent. (If this prominence increase, we can regard it as the beginning of spiral convolutions, Discospira.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.014.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 2. Trioniscus, Haeckel.

Definition.—Ring with three chambers, separated by three radial beams.

3. Archidiscus trioniscus, n. sp.

Ring triangular, roundish, equilateral, connected with the central chamber by three radial beams at equal distances (120°); therefore three equal ring chambers. (Resembles the central part of the disk of Tripodictya trigonaria, Pl. 42, fig. 8, and may be the ancestral form of it.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

4. Archidiscus trithalamus, n. sp.

Ring irregular, roundish, connected with the central chamber by three radial beams at unequal distances; therefore three ring chambers of different size. (If these differences be important, they introduce a spiral convolution in the further development of the Porodiscus arising from it.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.016.

Habitat.—South Pacific, Station 288, surface.

Subgenus 3. Tetroniscus, Haeckel.

Definition.—Ring with four chambers, separated by four radial beams.

5. Archidiscus stauroniscus, n. sp. (Pl. 48, figs. 9, 9a).

Ring regular, square, connected with the central chamber by four radial beams at equal distances, opposite in pairs in two axes perpendicular one to another; therefore four equal ring chambers (or congruent quadrants of the ring). Resembles the central part of the disk of Staurodictya medusa, &c. (Pl. 42, figs. 1-3); also of Staurodictya gracilis, Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3).

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

6. Archidiscus tetroniscus, n. sp.

Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not perpendicular one to another; therefore four ring chambers in pairs different, two opposite equal and larger than the two others.

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.016.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

7. Archidiscus tetrathalamus, n. sp.

Ring irregular, quadrangular, connected with the central chamber by four radial beams of increasing unequal length; therefore all four ring chambers of different size, gradually increasing in the following quadrants of the ring. Important as an ancestral type of such spiral and semi-spiral forms as Staurodictya cruciata (Pl. 42, figs. 4, 12, &c.) and Stylodictya clavata, Stylodictya stellata, &c., of Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. figs. 2, 7, 8, 9).

Dimensions.—Diameter of the ring 0.05 to 0.08, of the central chamber 0.06.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 4. Pentoniscus, Haeckel.

Definition.—Ring with five chambers, separated by five radial beams.

8. Archidiscus pentoniscus, n. sp.

Ring pentagonal or nearly circular, regular, connected with the central chamber by five radial beams of equal length and at equal distances (72°); therefore all five chambers of the ring of equal size and similar form. (Resembles the central part of the disk of Pentinastrum asteriscus, Pl. 44, fig. 2.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, surface.

Subgenus 5. Hexoniscus, Haeckel.

Definition.—Ring with six chambers, separated by six radial beams.

9. Archidiscus hexoniscus, n. sp. (Pl. 48, figs. 10, 10a).

Ring regular, hexagonal, or nearly circular, connected with the central chamber by six radial beams of equal length and at equal distances (60°); therefore all six chambers of the same size and form. (Resembles the central part of the disk of Hexinastrum geryonidum, Pl. 44, fig. 4.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

10. Archidiscus pyloniscus, n. sp. (Pl. 48, figs. 11, 11a).

Ring triangular, connected with the central chamber by six radial beams at alternating distances; therefore three larger chambers (of looser network) alternate with three smaller chambers (of denser network); pores of the former twice to three times as large as those of the latter. This species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these three larger ring chambers lose their few lattice-beams and so became open gates, we get Triolene or Triopyle, the original forms of the Pylodiscida.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

11. Archidiscus hexathalamus, n. sp.

Ring irregular, roundish, or hexagonal, connected with the central chamber by six radial beams of unequal increasing length; therefore all six ring chambers of gradually increasing size (beginning a spiral convolution, original form of some Discospira).

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.014.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Subgenus 6. Circoniscus, Haeckel.

Definition.—Ring with seven or more chambers, separated by seven or more radial beams.

12. Archidiscus octoniscus, n. sp.

Ring circular or regular octagonal, connected with the central chamber by eight equidistant radial beams; therefore eight ring chambers of equal size. (Compare the central part of the disk of Porodiscus quadrigatus, Pl. 41, fig. 3.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

13. Archidiscus polythalamus, n. sp.

Ring circular, connected with the central chamber by nine to ten or more radial beams at nearly equal distances. Ring chambers nine to ten, more or less equal, sometimes also eleven to twelve, more different. (This species is very variable, and may perhaps be divided into a number of different "transformistic species.")

Dimensions.—Diameter of the ring 0.04 to 0.06, of the central chamber 0.015.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2925 fathoms.

Genus 213. Axodiscus,^[252] n. sp.

Definition.—Porodiscida with a simple central chamber, surrounded by one single concentric ring, which is divided by radial beams into two to six or more radial chambers; margin of the disk armed with radial spines.

The genus Axodiscus differs from the preceding Archidiscus only in the shape of the margin of the small lenticular disk, which is armed with a variable number of radial spines, indicating certain axes or radii of the shell. If these marginal spines at certain equal distances from the margin branch and their distal ends become united by these branches forming a concentric second ring, the genus passes into Porodiscus. The different number and disposition of the marginal spines are probably very important, as determining the later development of two to four or more radii in the different genera of Porodiscida.

1. Axodiscus stylophorus, n. sp.

Ring circular, with two equal semicircular chambers, connected with the central chamber by two opposite radial beams, which are prolonged outside into two strong conical spines.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Axodiscus triradiatus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by three equidistant radial beams, which are prolonged outside into three short conical spines. (Differs from Archidiscus trioniscus in the possession of marginal spines.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

3. Axodiscus staurophorus, n. sp.

Ring regular, square, connected with the central chamber by four radial beams, which lie opposite in pairs in two perpendicularly crossed axes, and are prolonged outside into four delicate cylindrical spines.

Dimensions.—Diameter of the ring 0.045, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Axodiscus hexagonus, n. sp.

Ring regular, hexagonal, connected with the central chamber by six radial beams at equal distances, which are prolonged outside into six strong pyramidal spines.

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Axodiscus trigonus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by six radial beams of alternating length and distance; therefore three smaller (perradial) chambers (with denser and darker network) alternating with three larger (interradial) chambers (with looser and finer network). On the margin three strong conical radial spines, arising in the radius of the larger chambers. (Differs from Archidiscus pyloniscus, Pl. 48, fig. 11, mainly in the strong angular spines on the three corners of the triangular shell.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.014.

Habitat.—South Pacific, Station 296, depth 1825 fathoms.

6. Axodiscus octogonus, n. sp.

Ring circular or nearly octagonal, connected with the central chamber by eight radial beams at nearly equal distances, which are prolonged outside into eight short conical spines. (Differs from Archidiscus octoniscus in the marginal prolongation of the eight beams.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

7. Axodiscus spinosus, n. sp.

Ring circular, connected with the central chamber by ten to twelve radial beams at nearly equal distances, which are prolonged outside into short conical spines of variable length. (May be regarded as an aculeate variety of Archidiscus polythalamus.)

Dimensions.—Diameter of the ring 0.04 to 0.05, of the central chamber 0.014.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2950 fathoms.

Subfamily 2. Trematodiscida, Haeckel, 1862, Monogr. d. Radiol., p. 491 (sensu emendato et restricto).

Definition.—Porodiscida without radial appendages of the disk (solid spines or chambered arms on the margin), and without peculiar oscula on the margin of the disk, which is composed of two to four or more concentric rings.

Genus 214. Porodiscus,^[253] Haeckel, 1881, Prodromus, p. 459.

Definition.—Porodiscida with simple circular disk, composed of several rings (without radial appendages or peculiar oscula on the margin of the disk).

The genus Porodiscus is, next to its ancestral form, Archidiscus, the simplest and most primitive form of the Porodiscida, from which all other genera of this family can be derived. The disk is quite simple, without any marginal appendages, composed of a variable number of rings, commonly of circular form, sometimes more or less polygonal, elliptical, or irregular. In my Monograph (1862, pp. 491, 513) I had separated the species, here united in Porodiscus, into two different genera: Trematodiscus with concentric rings, and Discospira with spiral rings. But the extended study of these very common forms in a great number of specimens in the Challenger collection has convinced me that the separation of those two genera cannot be maintained. In one and the same locality, where one single characteristic disk-form is very common, we find intermingled quite regular disks with only concentric, circular rings (Trematodiscus), and other disks with one single perfect spiral ring (Discospira); and between these a smaller number of specimens, in which the rings of the disk are partly concentric, partly spiral; either the rings of the central part of the disk are concentric, the outer spiral (Perispira), or the proportion is inverse (Centrospira); and sometimes the whole disposition of the concentric and spiral rings is irregular, and the rings often interrupted (Atactodiscus). Therefore it appears more natural to give to all these different forms only the value of subgenera of Porodiscus, as I have already proposed in my Prodromus (1881, p. 459). Even the numerous species of Porodiscus (mainly characterised by the equal or different breadth of the rings, and by the number, form, and size of the connecting radial beams and of the superficial pores) are for the most part very variable and hard to distinguish, as all those characters are not constant. Porodiscus is a quite "transformistic genus."

Subgenus 1. Trematodiscus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

Definition.—All rings of the disk concentric (commonly circular, rarely a little elliptical or polygonal).

1. Porodiscus orbiculatus, Haeckel.

Trematodiscus orbiculatus, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 1.

Trematodiscus orbiculatus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers differing little in size, about as large as the central chamber. Pores regular, circular, two to two and a half on the breadth of each ring.

Dimensions.—Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.003.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados, Sicily, and Nicobar.

2. Porodiscus concentricus, Haeckel.

Trematodiscus concentricus, Haeckel, 1862, Monogr. d. Radiol., p. 493.

Trematodiscus concentricus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

Flustrella concentrica, Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 132; Ibid., 1875, p. 72, Taf. xxii. fig. 13.

? Flustrella concentrica, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 61, Taf. xx. fig. 42, Taf. xxi. fig. 51, Taf. xxxvi. fig. 29.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores regular, circular, one and half to two on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.003.

Habitat.—Fossil in many Tertiary rocks—Barbados, Sicily, Greece, &c.

Porodiscus haeckelii = Trematodiscus haeckelii, Bütschli, 1882, L. N. 41, Taf. xxiv. figs. 5a, 5b.

3. Porodiscus flustrella, n. sp. (Pl. 41, fig. 1).

Trematodiscus flustrella, Haeckel, 1866, MS. Canar. Ins.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores very irregular, polygonal, or roundish, one to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

Habitat.—Cosmopolitan; Atlantic, Pacific, &c., many Stations, surface.

4. Porodiscus sorites, Haeckel.

Trematodiscus sorites, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 2.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers different in size, increasing from the centre. Pores regular, circular, one to one and a half on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.006.

Habitat.—Mediterranean (Messina), surface.

5. Porodiscus macroporus, Haeckel.

Trematodiscus macroporus, Haeckel, 1879, MS.

Flustrella macropora, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers of different breadth, increasing from the centre. Pores regular, very large, nearly square, one single pore on the breadth of each ring.

Dimensions.—Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.005.

Habitat.—Fossil in the Tertiary rocks of Barbados.

6. Porodiscus microporus, Haeckel.

Trematodiscus microporus, Stöhr, 1880, Palæontogr., vol xxvi. p. 108, Taf. iv. fig. 17.

All rings of the disk concentric, either circular or a little elliptical; the innermost rings of the same breadth as the central chamber, the third ring much broader. Radial beams between them alternating; chambers of different size. Pores very small, subregular, everywhere of the same size, four to five pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the inner rings 0.02, of the outer 0.03; pores 0.0016.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

7. Porodiscus ellipticus, Haeckel.

Trematodiscus ellipticus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108, Taf. iv. fig. 16.

All rings of the disk concentric, either circular or a little elliptical, connected by eight piercing radial beams; central chamber elliptical, of the same breadth as the first ring, broader than the following rings, the breadth of which decreases towards the periphery. Pores irregular, in the inner rings twice as broad as in the outer (third) ring, four to five on the breadth of each ring.

Dimensions.—Diameter of the disk (with three rings) 0.18; breadth of the inner rings 0.03, of the outer 0.02; pores 0.003 to 0.006.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

8. Porodiscus heterocyclus, Haeckel.

Trematodiscus heterocyclus, Haeckel, 1862, Monogr. d. Radiol., p. 493, Taf. xxix. fig. 3.

? Flustrella cyclia, Harting, 1863, Fauna Banda-Zee, p. 11, pl. i. fig. 19.

Trematodiscus heterocyclus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk concentric, circular, connected by numerous radial beams, which are partly piercing, partly alternating. The breadth of the rings increases gradually from the centre towards the periphery, corresponding also to the size of the pores; two to three circular pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.007, of the sixth 0.02; pores 0.002 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

9. Porodiscus quadrigatus, n. sp. (Pl. 41, fig. 3).

All rings of the disk concentric, of nearly equal breadth, connected by four interradial beams, perpendicular one to another. The first ring (surrounding the central chamber) with eight chambers, the second only with four (alternating with the four radial beams). Size of the four chambers of each ring increases much towards the periphery. Pores regular, circular, about two on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.18; breadth of each ring 0.05; pores 0.004.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Subgenus 2. Perispira, Haeckel, 1881, Prodromus, p. 459.

Definition.—The inner rings of the disk concentric (commonly circular); the outer rings spirally convoluted.

10. Porodiscus perispira, n. sp. (Pl. 41, fig. 2).

Perispira perforata, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings nearly of the same breadth, connected by alternating irregular radial beams. Pores irregular, two to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of each ring 0.016; pores 0.003 to 0.005.

Habitat.—Pacific, central area, Stations 272 to 274, surface.

11. Porodiscus radiatus, n. sp.

Perispira radiata, Haeckel, 1881, Prodromus.

Inner rings of the disk (four or five) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings connected by piercing radial beams (eight in the inner half, sixteen in the outer half). Breadth of the rings and of the pores increasing from the centre towards the periphery, three to four pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.18; breadth of the second ring 0.006, of the eighth ring 0.02; pores 0.002 to 0.006.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 3. Centrospira, Haeckel, 1881, Prodromus, p. 459.

Definition.—The inner rings of the disk spirally convoluted, the outer rings concentric (commonly circular).

12. Porodiscus centrospira, n. sp. (Pl. 41, fig. 6).

Centrospira perispongidium, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) spirally convoluted (with simple or double spiral line), outer rings (three or four) concentric, subcircular. All rings nearly of the same breadth, connected by alternating radial beams. Pores subregular, two to three on the breadth of each ring. Lattice-work in the periphery of the disk a little spongy (as in Pl. 41, fig. 11).

Dimensions.—Diameter of the disk (with five rings) 0.15; breadth of each ring 0.015; pores 0.003.

Habitat.—Pacific, central area, Station 267, depth 2700 fathoms.

Subgenus 4. Discospira, Haeckel, 1862, Monogr. d. Radiol., p. 513.

Definition.—All rings of the disk spirally convoluted, forming parts of a simple or double spiral turning.

13. Porodiscus helicoides, Haeckel.

Discospira helicoides, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 7.

Trematodiscus helicoides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous alternating radial beams. Chambers little different in size, little longer than broad. Pores of equal size, regular, two on the breadth of each ring.

Dimensions.—Diameter of the disk (with ten rings) 0.2; breadth of each ring 0.01; pores 0.0025.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific; also fossil in the Tertiary rocks of the Mediterranean, Sicily, Oran, &c.

14. Porodiscus spiralis, Haeckel.

Flustrella spiralis, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 210; Mikrogeol., 1854, Taf. xix. fig. 62.

Discospira spiralis, Haeckel, 1862, Monogr. d. Radiol., p. 513.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous (twelve to sixteen) piercing radial beams. Chambers increasing in size from the centre towards the periphery. Pores irregular, of different size, one and a half to two on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.004.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; also fossil in the Tertiary rocks of Barbados, Sicily, Greece, &c.

15. Porodiscus operculina, Haeckel.

Discospira operculina, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 8.

All rings of the disk spirally convoluted around the central chamber, spiral line regular, simple. Breadth of the rings and length of the chambers increasing in size from the centre towards the periphery. Most part of chambers twice as long as broad. Pores irregular, of very different sizes, two to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.16; breadth of the rings 0.012 to 0.016; pores 0.002 to 0.006.

Habitat.—Mediterranean (Messina), surface.

16. Porodiscus bilix, Haeckel.

Discospira bilix, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf. vi. fig. 3.

All rings of the disk spirally convoluted around the large elliptical central chamber. Spiral convolutions of the inner rings simple, of the outer rings double; the latter twice as broad as the former. Pores regular, circular, in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, on the margin prominent.

Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.007, of the outer 0.013; pores 0.0017.

Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

17. Porodiscus bispiralis, Haeckel.

Stylodictya bispiralis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160. Taf. xxiv. fig. 1.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the rings; the fourth ring twice as broad as the first. Pores regular, circular; in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, prominent on the margin.

Dimensions.—Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.006, of the outer 0.012; pores 0.0015.

Habitat.—Fossil in the rocks of Barbados; living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

18. Porodiscus duplex, Haeckel.

Discospira duplex, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 4.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the broad rings. Pores regular, circular; in the inner rings two to three, in the outer four to five on the breadth. Radial beams interrupted. Margin of the rings thorny.

Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the rings 0.02 to 0.04; pores 0.007.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

19. Porodiscus semispiralis, n. sp. (Pl. 41, fig. 4).

All rings of the disk spirally convoluted, divided by four radial, perpendicularly crossed and zigzag shaped beams into four quadrants; the quarter rings of each quadrant halving the rings of each adjacent quarter. Half spiral line often irregular or partly interrupted. Breadth of all rings nearly equal. Pores irregular, roundish, two on the breadth of each ring. Margin of the disk dentated.

Dimensions.—Diameter of the disk (with nine rings) 0.22; breadth of each ring 0.012; pores 0.002 to 0.006.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 5. Atactodiscus, Haeckel, 1881, Prodromus, p. 459.

Definition.—Rings of the disk more or less irregular, partly concentric, partly spirally convoluted, often interrupted.

20. Porodiscus deformis, Haeckel.

Discospira deformis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 6.

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, increasing in breadth from the centre. Radial beams not piercing; pores regular, circular, two to six on the breadth of the different rings. (Very variable and irregular, sometimes more spiral, at other times more concentric, but always with equal pores.)

Dimensions.—Diameter of the disk (with four rings) 0.18; breadth of the first ring 0.014, of the second 0.03, of the fourth 0.06; pores 0.005.

Habitat.—Fossil in the Tertiary rocks of Barbados and Sicily; living in the Central Pacific, Stations 266 to 268, depths 2700 to 2900 fathoms.

21. Porodiscus irregularis, n. sp. (Pl. 41, fig. 7).

Atactodiscus irregularis, Haeckel, 1881, Prodromus, p. 459.

Perispongidium irregulare, Haeckel, 1878, MS. et Atlas (pl. xli. fig. 7).

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, with nearly equal breadth. Radial beams not piercing; pores irregular, roundish, two to four on the breadth of each ring; network in the periphery of the disk spongy. (Very variable and irregular, sometimes more spiral, at other times more concentric; disk in the peripheral part often more or less spongy. Differs from the preceding by the equal breadth of the rings and the different size of the pores.)

Dimensions.—Diameter of the disk (with six rings) 0.15; breadth of each ring 0.011; pores 0.002 to 0.004.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Barbados.

Genus 215. Perichlamydium,^[254] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with a simple circular disk (without radial spines and chambered arms), surrounded on the margin by a thin porous (but not chambered) equatorial girdle.

The genus Perichlamydium differs from Porodiscus only in the development of a thin, porous, equatorial girdle, which surrounds the circular margin of the chambered disk. This girdle lies in the equatorial plane of the lenticular disk, and represents a very delicate siliceous plate, perforated by numerous small pores. Sometimes the proximal part of the girdle is ribbed by thin radial beams, the distal prolongations of the radial rods of the central disk. If these ribs reach the margin of the girdle and are prominent over it, Perichlamydium passes over into Stylochlamydium.

1. Perichlamydium praetextum, Ehrenberg.

Perichlamydium praetextum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 21 (non 20).

Perichlamydium praetextum, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk (three to four) concentric, circular, of equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, nearly as broad as the disk; its circular pores of the same size as those of the disk; about two pores on the breadth of each ring.

Dimensions.—Diameter of the disk (without the girdle, with four rings) 0.11; breadth of each ring 0.012; breadth of the girdle 0.06 to 0.1; pores 0.004.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

2. Perichlamydium saturnus, n. sp. (Pl. 41, fig. 5).

All rings of the disk (three to four) concentric, circular (sometimes partly concentric, circular, partly spiral, or irregular), with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, about half as broad as the disk; its circular pores very small, scarcely half as large as those of the disk; about three pores on the breadth of each ring. (Very variable in the ring-form, differs from the preceding in the small pores of the girdle.)

Dimensions.—Diameter of the disk (without the girdle, with three rings) 0.11; breadth of each ring 0.02, pores 0.004, breadth of the girdle 0.05, pores 0.002.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

3. Perichlamydium accrescens, Haeckel.

Discospira accrescens, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 5.

All rings of the disk (six to seven) not concentric, convoluted in a simple spiral, of nearly equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle in the proximal part with numerous radial beams, which do not reach its margin; its pores half as large as those of the disk, where one to two pores arise on the breadth of each ring. (The girdle becomes twice to three times as broad as in the figure of Stöhr.)

Dimensions.—Diameter of the disk (with seven rings, without the girdle) 0.13; breadth of each ring 0.007 to 0.01; pores 0.0036; breadth of the girdle 0.05, pores of it 0.0017.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel); living in the Central Pacific, Station 266, depth 2750 fathoms.

4. Perichlamydium spirale, Ehrenberg.

Perichlamydium spirale, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 12.

All rings of the disk (three to four) not concentric, convoluted in a simple spiral, of increasing breadth from the centre; connected by numerous piercing radial beams. Equatorial girdle about half as broad as the disk, without radial beams; its pores of the same size as those of the disk, regular, circular; three pores on the breadth of the first ring, six pores of the fourth ring.

Dimensions.—Diameter of the disk (with four rings, without the girdle) 0.12; breadth of the first ring 0.01, of the fourth 0.02; breadth of the girdle 0.05; pores 0.003.

Habitat.—Fossil in the rocks of Barbados.

Subfamily 3. Ommatodiscida, Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

Definition.—Porodiscida without radial appendages of the concentrically annulated disk, but distinguished by one single or two opposite large marginal oscula, or wide openings on the margin of the disk, armed with a coronet of spines.

Genus 216. Ommatodiscus,^[255] Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

Definition.—Porodiscida without chambered arms and radial spines on the margin of the circular or elliptical disk, but with one large marginal osculum or opening surrounded by a coronet of spines.