﻿NT-.niRONAIAS 281 



I have never seen this variety, which seems to be shorter 

 than the type, and according to the figures, more distinctly 

 biangulate behind. 



Var. nephritica (Fischer and Crosse). 



Shell subrhomboid, somewhat arcuate, the base line being 

 incurved, scarcely biangulate behind, the almost rounded, low, 

 ])osterior ridge ending at the level of the base. 

 ^ IJnio calamitarum Sowkrijv, Conch. Icon., X\'I. 1868. pi. 



i.xxiv, fig. 385. 

 Unio calamitarum var. nephritica Fischer and Crosse. Miss, 



Sci., II, 1894, p. 613. 

 Unio cuprinns var. ncphriticns von Martens, Biol. Cent.. 



Amer., Moll., igoo, p. 505. 



It is quite probable that this is the male shell and that var. 

 arcuans is the female of one and the same thing, though this 

 form is much less biangulate behind. If this should be the case 

 the name arcuans would take precedence. 



Var. siibi'cntralis (von Martens). 



"Ventral margin distinctly convex. 



Long. 55, alt. vert. 2C), al?e 29, diam. 18 mm. \'ertices in 

 3/10 long." (von Martens.) 



Type locality, Mexico. 

 Unio ciiprinus var. subvcntralis von Martens, Biol. Cent. 



Amer., Moll, 1900, p. 506, pi. xxxvi, figs, i, icr, b. 



Nephronaias tabascoensis (Charpentier in Kuster). 



Shell somewhat elongated, subrhomboid, scarcely inflated, 

 solid, with a low, slightly double posterior ridge, which ends in 

 a feeble biangulation behind; beaks low, placed well forward, 

 their sculpture not observed ; surface sculptured with fine 

 concentric sulcations ; epidermis dark, rayless ; left valve with 

 two strong, radiating, somewhat split-up, pseudocardinals, a 

 rather wide, flat hinge plate, and two laterals, the lower the 

 heavier; right valve with one strong pseudocardinal and one 

 heavy lateral ; there are sometimes faint, oblique teeth between 

 them ; beak cavities compressed, rather deep, w'ith numerous 



