THE NAUTILUS. 47 



NEW aENEBA AND SPECIES OF CENTBAL AMEBICAN 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, ac- 

 cepted 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 indepen- 

 dently and from different points of view, the same species was 

 sometimes placed by them in diflferent 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 follow- 

 ing 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 and also the description of an unpublished species.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 plicatu- 

 lus, Kiister, 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 em- 

 braces two quite distinct groups, divisible as follows. 



Nephronaias (s. s) embraces plicatuh's, persvlcattis, meUeus, 

 dysoni, ortmanni, ravistellus, etc. Ample material of these two 

 latter species show that they are anatomically very closely allied 

 to EUiptio. There is no sexual difference of shape, and the gill 

 is gravid in its whole length. Nephronaias differs from EUiptio 

 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 gen- 

 erally rayed, and the gravid uterus is of Lampsiline type. 



The position of the dorsal scars within the beak cavities is 



