NEW EXOTIG UNIONID^. 389 



behind, polished, bbsoletely radiated ; cardinal teeth compressed, crenulate and 

 somewhat erect ; lateral teeth long and nearly straight ; nacre silver-white and 

 iridescent. 



Hah. — Uruguay River, South America, Prof. J. Wyman. 



My cabinet. 

 Diam. 1*2, Length 1/7, Breadth 2-7 inches. 



Shell smooth, subsulcate before, elliptical, iniiated, nearly equilateral, obtusely 

 angular behind, rounded before and slightly curved on the dorsal line; substance 

 of the shell rather thick, thicker before ; beaks a little prominent, with divergent 

 undulations at the tips ; ligament rather small, very dark-brown ; epidermis green- 

 ish-brown, darker behind, polished, obscurely rayed, with distant ma.rks of growth ; 

 umbonial slope much raised and rounded ; posterior slope wide, subsulcate, very 

 dark-green, almost black, somewhat carinate ; cardinal teeth compressed, long, crenu- 

 late, single in the right and double in the left valve ; lateral teeth long, striate and 

 nearly straight ; anterior cicatrices small, well impressed, confluent with the lower 

 but distinct from the upper; posterior cicatrices large, confluent and very slightly 

 impressed ; dorsal cicatrices placed across the centre of the cavity of the beaks ; 

 cavity of the shell deep and rounded ; cavity of the beaks shallow and rounded ; 

 nacre silver-white and iridescent. 



Remarks. — But a single specimen was received among the specimens from Prof. 

 Wyman. It is nearly allied to delodontus, Lam., and belongs to the same group, but 

 it is not so wide and has a smooth and darker epidermis. It is more ventricose and 

 more elliptical than Wymanii, herein described. The sulcations on the anterior 

 third are well marked, but they do not extend over the remainder of the disk, or 

 the species would be placed in the sulcate group. The beaks of this specimen are 

 so much eroded as only to leave a few of the divergent undulations, which prove 

 that they extended to the tip of the beaks. The epidermis is so well polished as to be 

 quite brilliant. The first mark of growth in this specimen forms a well-defined 

 yellow line ; the second one is of a very dark brown. In other specimens this cha- 

 racter will be likely to vary. 



Unio lepidus. PI. 50, fig. 306. 



Testa lacvi, elliptiea, subinflata, valde insequilaterali, posticd subrotundata, antice rotunda, ; valvulis 

 subtenuibus, antice* aliquantd crassioribus ; natibus proniinulis, ad apices rugose et divaricate undu- 

 latis ; epidermide polita, fusco-virentc, striata, radiata ; dentibus cardinalibus parviusculis, com- 

 pressis, obliquis ; latcralibus sublongis subcurvisque ; margarita. ca;rulco-alba et valde iridesceute. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, subrotund behind 

 and round before ; valves rather thin, slightly thicker before ; beaks somewhat 



99 



