DIPI.ODON 1273 



numerous subradial bars, which point downward and back- 

 ward, anterior end subtruncate ; surface finely, concentrically 

 striate ; epidermis brownish or brownish-green, banded, scarce- 

 ly shining ; left valve with two compressed pseudocardinals, 

 the hinder one feeble, and two delicate, curved laterals ; right 

 valve with one compressed pseudocardinal and a vestige of 

 another above it, with one lateral ; muscle scars impressed ; 

 nacre bluish, tinted yellow in the cavities. 



Length 28, height 20, diam. 13 mm. 



Guahyba, Brazil. 

 Unio iheringi Simpson, Syn., 1900, p. 894. 



This is a neat species, the smallest of the Diplodons and 

 quite distinct from all others. It is less drawn out behind than 

 either of the species placed in this group. 



T have not been able to discover whether this species has 

 ever been described or not. 



Group of Diplodon pazi. 



Shell subtrapezoidal, rounded in front and strongly biangu- 

 late behind ; the wavy beak sculpture extending well over the 

 disk ; epidermis olive ; pseudocardinals ragged, with a tendenc}^ 

 to break into denticles. 



Dtplodon pazi (Hidalgo). 



Shell unevenly ovate or subrhomboid. subsolid. convex, the 

 dorsal line curved; post-dorsal slope subtruncated ; posterior 

 ridge double below, ending a little above the base in a slight 

 biangulation ; post-dorsal region a little produced ; between this 

 and the posterior point the base line is feebly incurved ; beaks 

 apparently not high, their sculpture consisting of strong, sub- 

 nodulous, subradial ridges, the central ones coalescing; below 

 these ridges become somewhat zigzagged and they extend al- 

 most to the border of the shell ; later growth apparently des- 

 titute of sculpture ; epidermis olivaceous : pseudocardinals and 

 laterals granular ; nacre bluish-white. 



Length 2,7^ height 23 mm. 



Imbabura, Ecuador. 



