40 DESCRIPTION OF NEW 



margin, marks of growth rather distant and distinct; umbonial slope obtusely angular; 

 cardinal teeth rather large, double in the right and single in the left valve, crenulate, 

 pointed; lateral teeth short and straight; anterior cicatrices distinct; posterior cicatrices 

 distinct ; dorsal cicatrices small and placed on the under side of the plate between the 

 cardinal and lateral teeth ; cavity of the shell deep and rounded ; cavity of the beaks 

 rather deep and angular; nacre very white and very iridescent on the posterior portion 

 of the valve. 



Remarks. — There are three specimens before me of this small species. The largest is 

 scarcely an inch wide, but may not be entirely mature. It looks somewhat like U. decisus, 

 (Nobis,) but may be distinguished by its colour and by the place and form of the beak. 

 It is not an oblique species, but in outline more like U. glans, (Nobis.) In the yellow 

 colour of the posterior slope it resembles U. ehenus, (Nobis,) but it is not so rotund as 

 that shell, and has the beaks more medial. The posterior portion of the valve is remarka- 

 bly thin for so thick a species, and the nacre uncommonly pearly and iridescent. 



Unio nigrinus. pi. XXIV. Fig. 44. 



Testa Isevi, obovatd, sitbinflald, insequilaterali, nigra; valvulis tenuibus; natibus subprominentibus ; den- 

 tibiis cardinalibus parvis, acuminatis ; lateralibus longis curvisque; margaritd subpurpured et iridescente. 



Shell smooth, obovate, somewhat inflated, inequilateral, black ; valves thin ; beaks slightly prominent ; car- 

 dinal teeth small, pointed ; lateral teeth long and curved ; nacre somewhat purple and iridescent. 



Hab. West Florida, Major Le Conte. 

 Cabinet of Major Le Conte. 

 Diam. .7, Length LI, Breadth L9 inches. 



Shell smooth, reversely ovate, somewhat inflated, inequilateral, rounded before and 

 behind, black; substance of the shell thin; beaks slightly prominent and approaching the 

 anterior margin; ligament short and very thin; epidermis smooth, somewhat shining, 

 black, with very indistinct rays and approximate lines of growth ; cardinal teeth small, 

 double in both valves, pointed and more acuminate on the anterior division; lateral teeth 

 long, thin and curved ; anterior cicatrices distinct; posterior cicatrices confluent; dorsal 

 cicatrices placed in the centre of the cavity of the beaks; cavity of the shell rather deep 

 and rounded; cavity of the beaks shallow and slightly angular; nacre somewhat purple 

 and very iridescent posteriorly. 



Remarks. — A single specimen of this species, not very perfect, and eroded at the 

 beaks, was among the West Florida shells from Major Le Conte. In outline, it ap- 

 proaches U. ajnygdaliim, (Nobis,) but differs in being a larger shell, thinner, black on the 

 outside and purple within. It is not so purple as the U. ciiprinus, (Nobis,) nor is it so 

 light in the epidermis. It is also nearly allied to U. occultus, (Nobis,) but is not so wide 

 a species and is rounder on the umbonial slope. 



