﻿NKPHRONAIAS 267 



■'A''. Uncki can l)e readily separated from the other Nepliro- 

 naias of the region by its rugose sculpture, in which respect, 

 it resembles N. dysoni I,ea, from Costa Rica, and by its wavy, 

 radiating lines and the dark nacre." 



Nephronaias TiiHUANTiSPiiCKNSis (Crosse and Fischer). 



Shell inequilateral, elliptic rhomboid, moderately intiated, 

 solid,, concentrically sulcate ; posterior ridge rather prominent 

 and more or less double, ending behind in a slight biangula- 

 tion; epidermis tawny to brownish-black, rayless; ligament 

 brown; left valve with two solid, radial pseudocardinals and 

 two delicate laterals; right valve with one strong pseudocar- 

 dinal and an obsolete tooth above it with one strong lateral ; 

 miuscle scars well impressed ; dorsal scars under the hinge 

 plate ; nacre white, straw-colored or salmon. Male shell nearly 

 or quite straight on the basal line; female phell with a slight 

 marsupial swelling. 



Length 68, height 38, diam. 25 mm. 



Length 58, height 33, diam. 22 mm. 



San Efigenia, Oaxaca, Mexico; Capunta, Honduras, in the 

 Patook River. 

 Uiiio tchuantepeccnsis Crosse and Fischer, L de Conch., XLL 



1893, p. 296. — Fischer and Crosse, Miss Sci., II, 1894, p. 



618, ])1. Lxv, figs. 3, T^a, 4. 

 A'ephronaias tchiiantcpecensis Simpson, Syn., 1900, p. 594. 



An oblong, sometimes long ovate, shell, which is smoother, 

 more inflated and less biangulate behind than its near ally, 

 jV. copanensis. 



Nephronaias copanensis (von Martens). 



Shell subrhomboid, subinflated, very solid when old, inequi- 

 lateral, covered with a tawny brown or blackish, rough epider- 

 mis, which is generally sulcate : posterior ridge double, the 

 two ridges widely separated, usually angular and distinct and 

 ending behind in a decided biangulation ; beaks probably mod- 

 erately full, but in all the specimens seen very badly eroded 

 away : left valve with two strong, triangular, rag'ged pseudo- 



