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. ebenus, (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 nicrinus. Pl. XXIV. Fig. 44. 
Testa levi, obovata, subinflala, inxquilaterali, nigra; valvulis tenuibus ; natibus subprominentibus ; den- 
tibus cardinalibus parvis, acuminatis ; lateralibus longis curvisque; margarita subpurpurea 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 1.1, Breadth 1.9 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. amygdalum, (Nobis,) but differs in being a larger shell, thinner, black on the 
outside and purple within. It is not so purple as the U. cuprinus, (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. 
