96 CONCHOLOGIA CESTRICA. 
Shell, thin, smooth, elliptic-ovate, compressed, rounded 
anteriorly, produced and sub-angulated posteriorly ; dor- 
sal margin behind the ligament elevated, and compressed; 
epidermis more or less brown, or green, rays obsolete; 
nacre bluish-white, and iridescent. H. 1.25, W. 2.25, T. 
.75, inches. 
Station, Schuylkill River, Chester County. 
Family CORBICULIDA. 
Shell, bivalve, oval, or sub-triangular; primary teeth 
two, or three, in each valve; laterals two; ligament 
external. 
Animal, mantle lobes free in front, and at the base; 
siphons two; foot triangular, cylindrical, or linguiform ; 
tentacles small, triangular, pointed; gills broad, unequal, 
united posteriorly. 
DIAGRAM OF THE GENERA, AND SPECIES, OF THE FAMILY 
CORBICULIDE. 
FaMILy, GENUS. SPECIES. 
sulcatum, 
striatinum, 
stamineum, 
SPH2RLIUM fabalis, 
transversum, 
rosaceum, 
partumeium, 
CORBICULID. securis. 
virginium. 
Deon variabile, 
: abditum, 
compressum., 
Genus SPHAZERIUM, Scopo_l, 1777. 
Shell, oval, nearly equilateral, beaks prominent; two 
primary teeth in each valve; laterals elongated; liga- 
ment on the longer slope. 
Animal, with two short siphons, joined at base, oral 
tentacles short; foot narrow, elongated. 
Oss. — The small animals included in this family 
