﻿204 NEW UNIONID^ OF THE 



free nearly the whole length of the abdominal sack. Palpi small, subtriangular, 

 rather thin, united only at the upper posterior edges. Mantle very thin, thick and 

 colored along the whole margin, which has papillae for a short distance below the 

 branchial opening. Branchial opening rather small, with rather small brown papillae. 

 Anal opening small, with numerous very small light brown papillae on the inner edges. 

 Super-anal opening rather long, slightly colored and united below. Color of the mass 

 whitish. 



Embryonic shell elongate, pouch-shape, with indented sides. PL 5, fig. 5. 



Remarks. — This is a beautiful little species, rarely reaching one and a half inches in 

 width. I have seen one only out of about twenty specimens larger than the one 

 figured. That was subsequently sent to me by J. Postell, Esq., of St. Simon's Island, 

 who obtained it from the Chattahooche river. A single young specimen has the 

 beaks complete — all the others are eroded, some of them very much. The undulations 

 on thisn, umbering about eight, are very close and somewhat concentric. There is 

 much difference in the appearance of these specimens. Some are lighter and brighter 

 in the epidermis than others, and the rays extend sometimes over the whole disk, 

 while in others again they can be seen only on the posterior portion. It belongs to 

 the group of which acutissimus (nobis) may be considered the type, and is closer to 

 it than to Conradicus (nobis). It is a larger species than the former, and smaller 

 than the latter. It has rays of the same zig-zag character which belong to the group. 



Unto modicus. PL 24, fig. 86. 



Testa lsevi, obliqu3,,"subinflata, postice subbiangulatil, valde inequilaterali ; valvulis crassis, antice crassioribus ; 

 natibus subprominentibus, ad apices rugoso-undulatis ; epidermide tenebroso-fusca, eradiata; dentibus 

 cardinalibus subgrandibus crenulatisque ; lateralibus curtis, crassis subcurvisque ; margarita vel alba 

 vel pallido-salmoniS, et iridescente. 



Shell smooth, oblique, rather inflated, subbiangular behind, very inequilateral; 

 valves thick, thicker before ; beaks rather prominent, roughly undulate at the tips ; 

 epidermis dark brown without rays; cardinal teeth rather large and crenulate; 

 lateral teeth short, thick and somewhat curved ; nacre either white or pale salmon 

 color and iridescent. 



Proc. Acad. Nat. Sci., 1857, p. 171. 



Hab. — Chattahoochee River, near Columbus, Georgia. Bishop Elliott and G. 

 Hallenbeck. 



My cabinet and cabinets of Bishop Elliott and Mr. Hallenbeck. 

 Diam. '6, Length *9, Breadth 1-4 inches. 



Shell smooth, oblique, somewhat inflated, subbiangular behind, very inequilateral 

 and rounded before; substance of the shell thick, thicker before; beaks rather 

 prominent, with three or four large subcon centric undulations at the tip ; ligament 

 rather short, thick and brown ; epidermis dark brown, without rays, striate and with 



