426 NEW GENUS AND SOME NEW SPECIES 



1. Unio Ater. Plate VII. fig. 9. 



Testa ovatd, inaquilaterali, transversa, ventricosissimd ; umhonihus 

 elevatis ; natibus promhiulis ; ejndermide ritgosd nigrdque; umbonibus 

 elevatis; dentibus cardinalibus erectis, cristatis, later alibus granulatis, 

 rectisque; margaritd rosed. 



Shell inequilateral, ovate, transverse, much inflated ; umbones elevated ; 

 beaks slightly prominent; epidermis black and wrinkled; cardinal teeth 

 erect and crestlike, lateral granulated and straight; nacre rose colour. 



Hab. Mississippi below Natchez. T. W. Robeson. 



My Cabinet. 



Cabinet of Prof. Vanuxem. 



Diam. 2-6, Length 3, Breadth 4-5 inches. 



Shell very ventricose; margin ovate, wider behind, slightly 

 emarginate at base, and sometimes slightly truncate at poste- 

 rior margin ; substance of the shell thick ; beaks slightly pro- 

 jecting and decorticated ; ligament large ; epidermis black or 

 blackish, and wrinkled transversely; cardinal teeth erect, 

 crestlike, and double in both valves; lateral tooth curved, 

 long, deeply divided and slightly serrate, the interior division 

 emerging from the cavity of the beak ; posterior cicatrices 

 confluent, anterior cicatrices very distinct ; dorsal cicatrices 

 pass across the cavity of the beaks in a row* ; cavity of the 

 shell great; nacre pink and iridescent in the posterior margin. 



Remarks. — This shell is remarkable for the colour of its 

 epidermis and nacre. The perpendicular distance from the 

 cardinal tooth to the basal margin is very small, while that 

 from the posterior end of the lamellar tooth to the same mar- 

 gin is unusually great. It slightly approaches in form to 

 some varieties of the cariosus. 



* In a former paper of this volume, (page 262) I described the attaching mus- 

 cles of the back of the animal, the impressions of which in the shell I propose to 

 call dorsal cicatrices. 



