﻿ni':phr()naias 269 



much eroded in the only specimens seen ; Hgament very pale 

 brown or tawny ; surface generally slightly sulcate ; epidermis 

 tawny, rayless, with impressed or elevated radiating lines, 

 between which it is looped and wrinkled like dried paint ; left 

 valve with two small, stumpy, radiating pseudocardinals and 

 two curved laterals ; right valve with one solid pseudocardinal, 

 a small, compressed tooth above it and one lateral ; muscle 

 scars impressed, the anterior ones roughened ; pallial line dis- 

 tinct, marked with radiating sculpture ; nacre soiled white, 

 lurid in the cavity of the shell ; dorsal scars numerous, placed 

 under the hinge plate. 



Length 50, height 32, diam. 20 mm. 



Patook River, Honduras ; Rio del Miro, Nicaragua. 

 Nephronaias reticiilatiis Simpson, Pr. Ac. Sci. Phila., 1900, p. 



yy, pi. II, fig. 3 ; Syn., 1900, p. 595. 



The only specimens seen by the writer seem to differ from 

 all related species in having an almost evenly elliptical form. 

 The posterior end of the shell shows a narrow, scarcely per- 

 ceptible biangulation and the anterior end is narrowed into a 

 rounded point. It is also remarkable for the peculiar epider- 

 mal sculpture, much like that of Plagiola encarpus. The only 

 two shells I have seen are probably females. 



Group of Nephronaias aztcconim. 



Shell oblong, solid, incurved on the base, having the greatest 

 •diameter at or behind the middle ; beaks full ; pseudocardinals 

 small ; epidermis brown, sometimes faintly rayed ; female shell 

 with a well-developed marsupial swelling. Animal unknown. 



Nephronaias aztecorum (Philippi). 



Shell oblong, inequilateral, slightly inflated, the greatest 

 'diameter being at or behind the center, varying from subsolid 

 to solid, rounded in front, arcuate at the base ; beaks rather 

 liigh but generally subcompressed ; epidermis brown, some- 

 times feebly rayed ; pseudocardinals small ; laterals curved ; 

 nacre white or purple. 



