NEW GENERA AND SPECIES OF CENTRAL AMERICAN NAIADES.

BY L. S. FRIERSON.

In 1893 Messrs Crosse and Fischer divided the Mexican Naiades into quite a number of sections, to which they assigned names. Almost simultaneously (in 1900) von Martens and C. T. Simpson, in treating the Central American Naiades, accepted some of these sections of Crosse and Fischer, raising them to generic or subgeneric rank. Because of paucity of material, considerable diversity of opinion concerning the specific identity of several species may be noted in the works of these authors. Furthermore, their work of classification being done independently and from different points of view, the same species was sometimes placed by them in different genera.

Thanks to the arduous labors of A. A. Hinkley, who has again and again enriched our cabinets with material and data from these tropical countries, we are enabled to offer the following suggestions concerning some of the genera of these shells, and also the description of an unpublished species.

Nephronaias. This genus has for its type the Unio plicatulus, Küster, a species identified by von Martens as belonging to the Lampsiline shells, as aztecorum. Mr. Simpson however believed it to be nearly allied to the persulcatus, a markedly Unioid shell. In this the writer follows Mr. Simpson.

The genus Nephronaias as constituted by Mr. Simpson embraces two quite distinct groups, divisible as follows.

Nephronaias (s. s.) embraces plicatulus, persulcatus, melleus, dysoni, ortmanni, ravistellus, etc. Ample material of these two latter species show that they are anatomically very closely allied to Elliptio. There is no sexual difference of shape, and the gill is gravid in its whole length. Nephronaias differs from Elliptio in its sulcated disc, in its beak sculpturing, etc.

Included in Nephronaias by Simpson are, however, shells of a totally different type, such as medellinus, gundlachi, sapotalensis, etc. These latter are sexually dimorphic, smoother, more generally rayed, and the gravid uterus is of Lampsiline type.

The position of the dorsal scars within the beak cavities is 48different, in the examples of the pseudo Nephronaias seen by the writer. Nephronaias (s. s.) possesses an (accessory?) adductor scar attached to the frontal portion of the cardinal teeth, which is either absent or obsoletely marked in the second assemblage. For this latter group the writer, therefore, proposes to use the generic term of Actinonaias Crosse and Fischer, 1893, type U. sapotalensis Lea. The female of this species has been described by Dr. Ortmann (1912). Actinonaias embraces, besides the type, medellinus, gundlachi, (accepting Simpson’s interpretation of this latter species), and others.

Psoronaias, Crosse and Fischer (1893). This group of remarkable shells, embracing crocodilarum, psoricus, semigranosus, etc., was provisionally treated by Simpson as a group of Elliptio, but their remarkable sculpturing, and the deep beak cavities of some of their species, led him to observe that it was possible that the group should, after all, be placed in Quadrula.

I follow von Martens, in giving generic rank as above to the group. The type is Unio psoricus. To this genus we are enabled to add a species hitherto undescribed, under the name of

Psoronaias kuxensis, n. sp., PI. VII, figs. 1, 2.

Shell small, compressed, rough, brown, biangular. Length 50, height 30, diam. 17 mm.

Shell hyperbolically rounded before, the extreme frontal point below the centre. Dorsum slightly arched, descending behind the ligament to the widely biangular posterior; the upper angle of which is midway the height, the lower angle very little above the base, which is nearly straight. The beaks are small, low, acute, approximate; and apparently, concentrically ridged. Epidermis dark brown (olivaceous and obsoletely rayed in the young), rough, the lines of growth numerous and well impressed. The discs are covered with fine pustulations, more pustular in front, biradially linear behind. The post ridge is low, but distinctly double, making the shell biangulate behind. The teeth are double in the left valve, single in the right. The cardinals are deeply sulcate and stout. Laterals slightly curved or nearly straight, separated by an interdentum. Nacre purple, beak cavities rather deep. Dorsal scars numerous, 49extending in a row from above the centre of the cavity down and forward upon the base of the cardinal teeth. Three well impressed muscle scars in front, two behind, the latter almost confluent. Habitat, Kux Creek, Chama, Guatemala. Collected by Mr. A. A. Hinkley, Feb. 6, 1917. A few dead specimens were obtained on the bank of the Isaibha River (Chama) of which the Kux Creek is a tributary. Type in Academy Natural Sciences. Cotypes in collection of A. A. Hinkley, the author and U. S. N. Museum.

I place this species in Psoronaias Crosse and Fischer, type U. psoricus, because of its evident relationship to crocodilarum, and distinctus, differing mainly from the latter in size and degree of inflation, being much inferior in both respects to distinctus.