20 
APPENDIX. 
or concave, interstices of the ribs with a minute line, on the post-mnbonal 
slope these lines are larger and more prominent ; tine concentric lines 
crenulate the ribs. 
JV. filosa , pi. 4, tig. 3. Rhomboidal, comparatively short, ventricose ; 
ribs 30, slightly grooved, two or three about the umbonal slope more dis- 
tinctly grooved ; posterior margin behind the beak and umbo much curved ; 
umbonal slope angular* posterior slope slightly impressed ; end margin 
nearly straight. 
The figure represents a young specimen. The adult measures 1| inch, 
in length ; height 1£ inches. The posterior margin ot the figure is incor- 
rectly represented as emarginate, but it has a slight outward curve. 
MERCEXARIA. Schum. 
M. Carolinensis. Shell subtriangular, elongated, very inequilateral, 
slightly ventricose, disk with coarse, flattened, uneven, imbricated ridges 
on the middle and posterior side, the lines disposed to be ramose ; on the 
anterior side and posterior slope they are sharp, prominent, rugose, imbri- 
cated lines; lunule large, cordate. Length 5 inches; height 4 inches. 
Locality. CapeJFear river. 
LEPTOTHYRIS. Conrad. 
Shell equivalved, thin ; cardinal teeth compressed, divergirg from the 
apex with equal obliquity, one towards the anterior and the other to- 
wards the posterior ; anterior cardinal margin passing the apex and ending 
in an expansion or dentiform projection ; fulcrum excavated, which exca- 
vation extends behind the expanded cardinal termination under the apex ; 
pallial sinus extending rather beyond the middle of the valves, slightly 
ascending and truncated at the inner end. 
L. parilis, pi. 3, fig. 9. Shell oval, ventricose, equilateral, summit 
prominent; base truncated medially, umbonal slope subangular ; post- 
umbonal slope flattened, much depressed ; disk with obscure concentric 
slightly impressed broadTurrows ; posterior end truncated. 
There is but one valve of this shell in the State Cabinet, but the hinge 
is so peculiar that I could not refer it to any genus known to me. 
CARDIUM. 
/Subgenus traciiycardium. 
T. helium. Shell slightly oblique, suboval, profoundly vetricose, ribs 
profoundly elevated, narrow, slightly oblique or turned towards the ante- 
