Note 4 — CHAP. XIV. WE EXPLORE THE TANGANYIKA LAKE.

The following Paper by S. P. Woodward, F.G.S., communicated by Prof. Owen, appeared in the Proceedings of the Zoological Society of London, June 28, 1859.

The four shells which form the subject of the present note were collected by Captain Speke in the great freshwater lake Tanganyika in Central Africa.

The large bivalve belongs to the genus Iridina, Lamarck,—a group of river mussels, of which there are nine reputed species, all belonging to the African continent. This little group has been divided into several sub-genera. That to which the new shell belongs is distinguished by its broad and deeply-wrinkled hinge-line, and is called Pleiodon by Conrad. The posterior slope of this shell is encrusted with tufa, as if there were limestone rocks in the vicinity of its habitat.

The small bivalve is a normal Unio, with finely sculptured valves.

The smaller univalve is concave beneath, and so much resembles a Nerita or Calyptræa that it would be taken for a sea-shell if its history were not well authenticated. It agrees essentially with Lithoglyphus,—a genus peculiar to the Danube; for the American shells referred to it are probably, or, I may say, certainly distinct. It agrees with the Danubian shells in the extreme obliquity of the aperture, and differs in the width of the umbilicus, which in the European species is nearly concealed by the callous columellar lip.

In the Upper Eocene Tertiaries of the Isle of Wight there are several estuary shells, forming the genus Globulus, Sow., whose affinities are uncertain, but which resemble Lithoglyphus.

The lake Tanganyika (situated in lat. 3° to 8° S. and long. 30° E.), which is several hundred miles in length and 30 to 40 in breadth, seems entirely disconnected with the region of the Danube: but the separation may not always have been so complete, for there is another great lake, Nyanza, to the northward of Tanganyika, which is believed by Speke to be the principal source of the Nile.

The other univalve is a Melania, of the sub-genus Melanella (Swainson), similar in shape to M. hollandi of S. Europe, and similar to several Eocene species of the Isle of Wight. Its colour, solidity, and tuberculated ribs give it much the appearance of a small marine whelk (Nassa); and it is found in more boisterous waters, on the shores of this great inland sea, than most of its congeners inhabit.

1. Iridina (Pleiodon) Spekii, n. sp. (Pl. XLVII. fig. 2.)

Shell oblong, ventricose, somewhat attenuated at each end: base slightly concave; epidermis chestnut brown, deepening to black at the margin; anterior slope obscurely radiated; hinge-line compressed in front and tuberculated, wider behind and deeply wrinkled.

Length 4³⁄₄, breadth 2, thickness 1³⁄₄ inches.

Testa oblonga, tumida, extremitatibus fere attenuata, basi subarcuata; epidermide castaneo-fusca, marginem versus nigricante; linea cardinali antice compressa tuberculata, postice latiore, paucis rugis arata.

2. Unio Burtoni, n. sp. (Pl. XLVII. fig. 1.)

Shell small, oval, rather thin, somewhat pointed behind; umbones small, not eroded; pale olive, concentrically furrowed, and sculptured more or less with fine divaricating lines; anterior teeth narrow, not prominent; posterior teeth laminar; pedal scar confluent with anterior adductor.

Length 12, breadth 8¹⁄₂, thickness 5¹⁄₂ lines.

Testa parva, ovalis, tenuiuscula, postice subattenuata; umbonibus parvis, acuminatis; epidermide pallide olivacea; valvis lineolis divaricatis, decussatum exaratis; dentibus cardinalibus angustis, haud prominentibus.

3. Lithoglyphus zonatus, n. sp. (Pl. XLVII. fig. 3.)

Shell orbicular, hemispherical; spire very small; aperture large, very oblique; umbilicus wide and shallow, with an open fissure in the young shell; lip continuous in front with the umbilical ridge; columella callous, ultimately covering the fissure; body-whirl flattened, pale olivaceous, with two brown bands, darker at the apex; lines of growth crossed by numerous oblique, interrupted striæ.

Diameter 5-6, height 3 lines.

Testa orbicularis, hemisphærica, late umbilicata (apud juniores rimata), spira minuta; apertura magna, valde obliqua; labio calloso (in testa adulta rimam tegente); pallide olivacea, fasciis duabus fuscis zonata; lineis incrementi striolis interruptis oblique decussatis.

4. Melania (Melanella) nassa, n. sp. (Pl. XLVII. fig. 4.)

Shell ovate, strong, pale brown, with (sometimes) two dark bands; spire shorter than the aperture; whirls flattened, ornamented with six brown spiral ridges crossed with a variable number of white, tuberculated, transverse ribs; base of body-whirl eight with tuberculated spiral ridges variegated with white and brown; aperture sinuated in front; outer lip simple; inner lip callous.

Length 8¹⁄₂, breadth 5¹⁄₂ lines.

Testa ovata, solida, pallide fusca, zonis 2 nigricantibus aliquando notata; spira apertura breviore; anfractibus planulatis, lineis 6 fuscis spiralibus et costis tuberculatis ornatis; apertura antice sinuata; labro simplici; labio calloso.

P.S. July 27th.—In addition to the foregoing shells, several others were collected by Capt. Speke, when employed, under the command of Capt. Burton, in exploring Central Africa in the years 1856-9; these were deposited in the first instance with the Geographical Society, and are now transferred to the British Museum.

A specimen of Ampullaria (Lanistes) sinistrorsa, Lea, and odd valves of two species of Unio, both smooth and olive-coloured, were picked up in the Ugogo district, an elevated plateau in lat. 6° to 7° S., long. 34° to 35° E.

A large Achatina, most nearly related to A. glutinosa, Pfr., is the “common snail” of the region between lake Tanganyika and the east coast. Fossil specimens were obtained in the Usagara district, at a place called Marora, 3000 feet above the sea, overlooking the Lufiji River, where it intersects the coast range (lat. 7° to 8° S., long. 36° to 36° E.).

Another common land snail of the same district is the well known “Bulimus caillaudi, Pfr.,” a shell more nearly related to Achatina than Bulimus.

Captain Speke also found a solitary example of Bulimus ovoideus, Brug., in a musjid on the island of Kiloa (lat. 9° S., long. 39° to 40° E.). This species is identical with B. grandis, Desh., from the island of Nosse Bé, Madagascar, and very closely allied to B. liberianus, Lea, from Guinea.

[5] Captain Balfour, H.M.I.N., who kindly supplied me with a list of necessaries for sail-making and other such operations on the Lake. I had indented upon the Engineers’ Stores, Bombay, for a Massey’s patent or self-registering log, which would have been most useful had the people allowed it to be used. Prevented by stress of business from testing it in India, I found it at sea so thoroughly defective, that it was returned from whence it came by the good aid of Captain Frushard, then commanding the H.E.I.C.’s sloop of war Elphinstone. I then prepared at Zanzibar, a line and a lead, properly hollowed to admit of its being armed, and this safely reached the Tanganyika Lake. It was not useless but unused: the crew objected to its being hove, and moreover—lead and metal are never safe in Central Africa—the line, which was originally short, was curtailed of one half during the first night after our departure from Kawele. It is by no means easy to estimate the rate of progress in these barbarous canoes barbarously worked. During the “spirts” when the paddler bends his back manfully to his task, a fully-manned craft may attain a maximum of 7 to 8 miles per hour: this exertion, however, rarely exceeds a quarter of an hour, and is always followed by delay. The usual pace, when all are fresh and cool, is about 4 to 5 miles, which declines through 4 and 3 to 2¹⁄₂, when the men are fatigued, or when the sun is high. The medium, therefore, may be assumed at 4 miles for short, and a little more than 2 miles an hour for long trips, halts deducted.