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 strisB, and imbricating lines of growth near the 

 margin. 



This species has been observed only in a single imperfect ventral valve ; hut 

 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 

 area, while the bifurcating plications of the siinis furnish ready means of distin- 

 guishing it from any other except the ^S". arenosa, which has a much more shallow 

 sinus with less elevated beak and broader umbo. The plications are likewise more 

 slender than those of that species in the Oriskany sandstone, and the surface is 

 marked by fine radiating strije, a teature which I have not observed in that one. 



This species differs from <S'. divaric.ata (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. 



Spiiifera disparilis. 



PLATE XXX. 



Spirxfer ditparilU : Hail, Tenth Report on the State Cabinet, p. 134. 1857. 

 " " Description of New Species Pal. Fossils, p. 94. 1867. 



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. 



