NEW EXOTIC UNIONIDiE. 385 



teeth rather small, compressed and crenulate ; lateral teeth rather long and nearly 

 straight, nacre silver-white and iridescent. 



Hob. — Uruguay Kiver, South America, Prof. J. Wyman. 



My cabinet. 

 Diam. -8, . Length 1-3, Breadth 1-7 inch. 



Shell smooth, subrotund, inflated behind the umbonial slope, very inequilateral, 

 obtusely subangular behind and obliquely rounded before ; substance of the shell 

 somewhat thick, slightly thicker before ; beaks slightly prominent and inflated ; 

 ligament small and dark-brown ; epidermis striate, blackish-green, eradiate, with 

 rather distinct lines of growth ; umbonial slope slightly raised and obtusely angular ; 

 posterior slope rather wide, with a small carina ; cardinal teeth rather small, com- 

 pressed, crenulate and somewhat erect ; lateral teeth rather long and nearly straight ; 

 anterior cicatrices rather small, well impressed, confluent with the lower but distinct 

 from the upper ; posterior cicatrices rather large, confluent and slightly impressed ; 

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

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

 silver-white and iridescent. 



Remarks. — This seems to be a small species. There are two specimens before me, 

 the smaller about half the size of the larger, which is about an inch and three- 

 quarters wide. It is nearly allied to Paranensis and belongs to the same group. It is 

 not quite so round, and the swelling is more sudden before the umbonial slope. It 

 has not the well defined arch between the cardinal and lateral teeth, which many 

 of this group haj§e. The epidermis is very dark bottle-green, almost black, but not 

 so black as nodurnus, from which it also differs in being not so round nor so much 

 compressed. The beaks are not perfect enough in my specimens to observe undula- 

 tions, but the nacre indicates at the tip that they had the usual divergent cost;©. In 

 both there are imperfect irregular undulations along the angle of the posterior slope, 

 which may not, however, be persistent. 



Unio discdlus. PI. 44, fig. 293. 



Testa laevi, subrotunda, valde compressa, valde intequilaterali, antice et postice rotundata; valvulis crassius- 

 culis, antice aliquanto erassioribus ; natibus subproinincntibus, ad apices aliquanto divaricate undu- 

 latis ; epidcrmide tencbroso-castanea, minute striata obsolete radiataque ,- dontibus cardinalibus 

 parviusculis, lamellatis crcnulatisque ; lateralibus sublongis, striatis curvisque ; magarita alba ct 

 iridescente. 



Shell smooth, subrotund, very much compressed, very inequilateral, rounded be- 

 fore and behind; valves somewhat thick, slightly thicker before; beaks somewhat 

 prominent, with small divergent undulations at the tips ; epidermis dark chestnut- 



9S 



