﻿Nl'PTlRONAIAS 



255 



of the female is as greatly developed as in any species of 

 Lampsilis. In a few instances where I have been able to exam- 

 ine only a single form of a species I could not be positive 

 whether it should be placed here or in Unio. The whole group 

 is a difficult one and I have found great variation of specimens 

 among the species and comparatively few shells that at all 

 perfectly agree with the published figures or descriptions. 



Group of Kcphronaias medellina. 



Shell scarcely sulcate, shining, rather brightly rayed, dis- 

 tinctly biangidate behind, solid, swollen; beaks rather full, 

 with delicate sculpture ; pseudocardinals solid, stumpy, tri- 

 gonal ; laterals heavy, somewhat club-shaped; nacre rich and 

 soft, silvery or purple; female shell consideralbly inflated at 

 the post-basal region, and differing somewhat from that of 

 the male. 



Nephkonaias medellina (Lea). 



Shell long-rhomboid, solid, subinflated, with a rather high,, 

 rounded posterior ridge, which is slightly double below and 

 ends in a wide subtruncation ; posterior slope obliquely trun- 

 cate; beaks only moderately full and high, their sculpture not 

 observed ; posterior slope often having slight plications or cor- 

 rugations, the rest of the shell nearly smooth. Surface green- 

 ish, darker above, with faint, somewhat wavy, wide or narrow 

 rays ; left valve with two strong, ragged pseudocardinals and 

 one strong lateral : right valve with one pseudocardinal and a 

 small tooth in front of and another behind it, and one lateral ; 

 sometimes the laterals are more or less subdivided ; beak cav- 

 ities shallow ; muscle scars smooth, not deep ; nacre purple, 

 reddish or salmon. The female shell is somewhat inflated at 

 the post-basal part ; the male shell is slightly arcuate. 



Length 70. height 39, diam. 25 mm. 



State of Vera Cruz. Mexico. 



? Unio purpuriatus Say, New Harm. Diss., (newspaper form), 

 January 15, 183 1. 



