ORISKANY SANDSTONE. 
451 
these there is a third (usually) smaller depressed plication, with a shal¬ 
low sinus below the middle of the shell. On the dorsal valve the two 
central plications, below the middle, are a little stronger and more 
widely separated from the lateral ones, rising in front into a slight 
mesial elevation. When seen from the front, the margin of the shell 
presents a very distinct sinus, with a corresponding projection of the 
opposite valve, the entire margin being deeply serrate. The liner surface 
markings are mostly obliterated, some imbricating lines of growth alone 
remaining. 
The fimbriated appendage along the hinge-line has been observed in 
so many specimens, that I can only suppose it to belong to the animal 
economy. The remains of this appendage are sometimes observed upon 
the inner margins of the separated valves. 
This species differs from the preceding in the proportionally wider and less sloping 
cardinal line, and in the less extension of the beak of the ventral valve, which is 
smaller and more neatly defined; in the fewer plications and comparatively greater 
convexity of the ventral valve, while the dorsal valve is slightly convex and ab¬ 
ruptly inflected at the margin, features not observable in L.Jlabellites. 
In the localities where this species occurs, often in large numbers, few or no 
specimens of the L. fiabellites are found; Avhile in localities where the surfaces of 
the layers are covered with the latter shell, no specimens of L.fimbriata have been 
seen. 
Fig. 2 a, b. Dorsal and profile views of a specimen of ordinary size. 
Fig. 2 c. Front view of a specimen a little greater than the ordinary size, and which has the 
fimbriated expansion extending below the cardinal angles. 
Fig. 2 d. The ventral side of the preceding specimen, enlarged two diameters. 
Fig. 2 e. The interior of the ventral valve, showing the cardinal teeth and the muscular 
impression. 
Fig. 2 e. The interior of the dorsal valve, showing the muscular impression, the cardinal 
process, the oblique lamella, median septum and bases of the crural processes. 
Fig. 2 f. The same enlarged. 
Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 
