﻿NEvPIIRONAIAS 279 



left valve and two in the right ; two laterals in the left valve 

 and one in the right ; pseudocardinals showing a disposition 

 to blend together and become tuberculous in the old shells ; 

 anterior scars impressed ; posterior scars round, superficial ; 

 nacre bluish-white or white. 



In the type, an old male shell, the base is almost straig^ht. 

 In three younger shells in the National Museum collection the 

 post-basal region is slightly produced. 



Length 107, height 57, diam. 34 mm. 



Length 03, height 50, diam. 2() mm. 



Guatemala, Rio de las Salinas ( Stoll ) , and Systeme de Po- 

 lochic (von Ihering). 

 Unio microdon von Martens, Biol. Cent. Am., Moll., 1900, 



p. 504. pi. XXXV, figs. I, la-c. 



I am not positive as to the systematic position of this species 

 as I am not certain that the young, somewhat broken and erod- 

 ed shells in the National Museum collection are the same as 

 von Martens' species. One of these is as large as N. calaini- 

 tarum and resemWes it somewhat, but is much thinner and is 

 evidently a young shell. It appears to show something of the 

 blending together of the pseudocardinals, which is so marked 

 a character in von Martens' shell. A younger fresh valve 

 shows faint rays and a bluish-white nacre. 



Nephronaias CALA.MiT.viiUM ( Morelct ) . 



Shell very inequilateral, subcompressed, rather solid, some- 

 what elongated and subrhomboid, with a low, rounded or 

 feebly biangulate posterior ridge ; beaks scarcely elevated, 

 compressed but sharp, their sculpture consisting of fine, con- 

 centric ridges, which are sometimes feebly corrugated and 

 doubly looped, this sculpture gradually passing into the fine, 

 concentric ridges that cover the surface of the shell ; there is 

 often a radiating groove on the posterior slope and this is 

 sometimes replaced by a feeble, dark ray ; there are occasion- 

 ally a few faint rays behind on the younger shells, otherwise 

 the surface is yellowish-green in the young and darker in the 

 old specimens ; left valve with two triangular, radial, some- 



