204 
PALAEONTOLOGY OF NEW-YORK. 
The surface is marked by about twenty or twenty-one somewhat slen¬ 
der low rounded simple plications on either side; while the mesial fold 
has seven or eight plications in its upper part, which bifurcate, and 
become twelve or fourteen at the anterior margin. The entire surface is 
marked by fine radiating striae, and imbricating lines of growth near the 
margin. 
This species has been observed only in a single imperfect ventral valve ; but 
its characters, in the individual, are quite distinct from any other species in this 
formation ; the lateral plications are more numerous than in any other, with a low 
strea, while the bifurcating plications of the sinus furnish ready means of distin¬ 
guishing it from any other except the iS. arenosci , which has a much more shallow 
sinus with less elevated beak and broader umbo. The plications are likewise more 
slender than those of that speciesdn the Oriskany sandstone, and the surface is 
marked by fine radiating striae, a feature which I have not observed in that one. 
This species differs from S . divaricata (which has likewise plications in the sinus) 
in the general contour of the shell, the deeper sinus and the simple plications on 
the lateral portions of the shell, as well as the more minute surface marking, 
which is quite distinctive. 
Geological formation and locality. In the Corniferous limestone, near Clarence 
hollow, Erie county, New-York. 
Spirifera disparilis. 
PLATE XXX. 
Spirifer disparilis ; Hall, Tenth Report on the State Cabinet, p.134. 1857. 
“ “ Description of New Species Pal. Fossils, p. 94. 1857. 
Shell small, somewhat semielliptical; length and breadth about as two 
to three or three to four : hinge-line a little less than the greatest 
width of the shell; cardinal extremities rounded. 
Ventral valve gibbous, extremely elevated towards the umbo, abruptly 
curving to the front, and sloping in a nearly straight or slightly 
concave line to the cardinal extremities : sinus deep and angular; 
beak extremely elevated, and abruptly incurved over the high nar¬ 
row fissure. Area high, triangular; margin rounded, the width about 
twice the height. 
