SPIRIFERiE OF THE HAMILTON GROUP. 
221 
Spirifera sculptilis. 
PLATE XXXV. 
Delthyris sculptilis : Hall, Geol. Report of Fourth District New-York, p. 202. 1843. 
Shell gibbous; valves subequally convex, semielliptical or subtriangular : 
hinge-line longer than the width of the shell, and prolonged into 
mucronate extensions; length about half the width on the hinge-line. 
Surface coarsely plicated. 
Ventral valve regularly convex, arcuate; beak arcuate over a sublinear 
area of moderate height, extending to the limits of the cardinal line ; 
mesial sinus strongly defined, subangular. 
Dorsal valve regularly convex, the greatest convexity in the middle 
and regularly arcuate from beak to base; mesial fold abruptly and 
strongly elevated, with the summit flattened or 'grooved; beak in¬ 
curved : area very narrow. 
Surface strongly marked by three, four or five abruptly elevated angular 
plications on each side of the mesial fold and sinus, leaving a some¬ 
what wide corrugated space at the cardinal angles. The plications 
bordering the sinus are stronger, more elevated, and continuing dis¬ 
tinct quite to the apex.. The shell is concentrically marked by strong 
imbricating lamellose striae, which are abruptly bent backwards and 
much elevated in crossing the plications, giving them a subnodose 
character. In the bottom of the sinus, these lamellose striae have often 
a distinct retral bend, with a slight elevation indicating an incipient 
plication which corresponds with the depression in the mesial fold. 
This species is readily recognized by its few strong plications, and the wide 
space at the cardinal extremities marked only by the concentric stri®. Compara¬ 
tively few specimens have been found, and these are partially exfoliated. 
In the figures illustrating this species, the dorsal valve is a cast. 
Geological formations and localities. This shell, in its characteristic form, 
occurs in a calcareous layer in the Hamilton shales, at Eighteen-mile creek. It is 
found at Ludlowville in Cayuga county ; on the east and west shores of Seneca 
lake, and at York in Livingston county. 
