9 © 
PALAEONTOLOGY OF NEW-YORK. 
single dorsal valve, recognized as of this species, the cardinal process is 
slender, the parts narrowly diverging, and continued in a narrow rounded 
elevation to the middle of the valve. No defined muscular impressions 
are visible in this specimen. 
The figures 9, 10 & 11, Plate XII, and figures 1 - 5, Plate xm, illustrate some of the 
usual forms and the preceding characters of this species. 
Notwithstanding that these characters can be traced through the various stages 
of growth offering differences from the ordinary forms of S. inequiradiata, there 
may still remain some doubt whether a large collection may not show intermediate 
forms which will unite the two. 
The Leptcena stephani of Barrande has a similar wrinkled surface in some of the 
individuals, though the intermediate finer striae are not shown in the figures. In 
these two shells, the muscular impressions are quite distinctive ; and the figure 7 b , 
Plate x, Barrande, approaches in character to some varieties of S. inequiradiata. 
Some varieties of the species under consideration may be compared with S. cor- 
rugata , Portlock sp. (not of Conrad). 
The species differs in form of shell, character of striae, and muscular impressions, 
from the S. inequiradiata. 
Geological formation and locality. Rarely in Schoharie grit, but not uncommon 
in the Corniferous limestone, in the Helderberg mountains, Schoharie; in Ontario 
county; and at Stafford in Genesee county and Williamsville in Erie county. It 
has likewise been recognised among the collections made at the Bake-oven on the 
Mississippi river, in Illinois. 
i 
Strophodonta hemispherica. 
PLATE XIV. 
Strophomena ( Strophodonta) hemispherica : Hall in Tenth Eeport on the State Cabinet, p. 113. 1857. 
Shell subhemispheric, semielliptical in outline : binge-line equalling or 
greater than the width of the shell; cardinal extremities sometimes 
salient and auriculate; length and breadth about as four to five : in 
the larger specimens the length is about two inches, with a breadth 
of two and a half inches. Ventral valve gibbous, the elevation of the 
curvature being often equal to half the length of the shell, sometimes 
very abruptly declining to the front : umbo moderately, or sometimes 
more extremely elevated; apex incurved; area narrow; margin ere- 
