112 
PALAEONTOLOGY OF NEW-YORK. 
strige are of the character of S. inequistriata, S. textilis and others, a condition 
sometimes assumed by S. perplana in the Hamilton shales of Iowa; hut we have 
that species in the same association with this one, showing its characteristic 
muscular impressions, with a somewhat wider area than S. mucronata , and the 
surface striae even or raised at intervals into elongate' nodes, but never having 
the elevated strige and equal interspaces with finer strige shown by this species. 
Although it is not always (and in some localities not often). produced at the 
hinge-extremities, it is the only form which I can identify with Mr. Conrad’s 
description. The S. elmira is too convex on the ventral valve, and moreover rarely 
occurs except in casts which give the strong muscular impression a prominence 
that would not have been overlooked in the description. 
Figures 5 and 5 a, Report (p. 266) of the 4th District of New-York, are of this species, 
and not identical with 5 b, c, which are of the S. cayuta. 
The figure given by Mr. Vanuxem (Geol. Report of the 3d District, page 174, figure 1) 
is of this species, found in the neighborhood of Ithaca. 
Geological formation and localities. In the Chemung group, at Chemung-narrows; 
at the Inclined plane of the railroad near Ithaca; near Elmira and Bath ; and 
also at Cortlandville and many other localities in the central and southern parts 
of the State. 
Strophodonta coelata (n. s.). 
PLATE XIX. 
Shell resupinate, semielliptical or semicircular; the cardinal extremities 
extremely produced. 
The cast shows that the ventral valve is concave, being moderately 
convex upon the umbo, and sloping gently downwards to below the 
middle ; beyond which, the anterior portion is abruptly deflected. 
The area is of moderate width, flat and striated, with the margin crenu- 
lated for nearly its entire length; the crenulations elongate and a 
little oblique. 
The divaricator muscular impressions form a broad flabelliform scar, 
which is once and a half as wide as long, and has been nearly surrounded 
by an elevated rim. Each division is marked by eight or nine distinct 
lobes. The occlusor impressions occupy semioval spots in the upper part 
of this area, and are separated by a narrow ridge, which becomes broader 
