Lower South Bay, Oneida Lake, N. Y., collected by F. C. Baker, 1916.
This species is typically narrower than A. lustrica Pils., with a smaller aperture and shorter whorls; but it is chiefly distinguished by the more convex whorls (deeper suture), and the rounded instead of angular posterior end of the aperture. In Paludestrina nickliniana the last whorl is much longer. Possibly it may be a subspecies of lustrica, yet it has so distinct an appearance that a special name seems desirable. There are also wider examples, which still differ from lustrica by the deeper suture and aperture.
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to offer the following suggestions concerning some of the genera of these shells, and also the description of an unpublished species.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.