CYRTINA OF THE HAMILTON GROUP. 
267 
valves, the spires may be directed towards the cardinal extremities as 
in Spirifera. 
The original specimen described was too imperfect to admit of a full description, 
but the characters indicated have been observed in all the specimens obtained. 
The illustrations, Plate xxvn, figs. 5-10, represent the prevailing features of 
the species. 
. Geological formations and localities . This species occurs in the Schoharie grit, 
in Albany and Schoharie counties; and in the Corniferous limestone, at Williams- 
ville in Erie county. I have also a specimen from the same rock in Michigan, re¬ 
ceived from Dr. Rominger of Ann-Arbor. Although having so wide a geographical 
range, this species is a rare fossil. 
Cyrtina crassa (n. s.). 
PLATE XXVII. 
Shell depressed-pyramidal (semielliptical in a dorsal view); length and 
breadth about as three to four; hinge-line equal to the greatest width 
of the shell, with the extremities slightly rounded. 
Ventral valve depressed-semipyramidal, convex, regularly arching from 
the beak and cardinal area to the front; sinus broad and rounded in 
the bottom ; beak extended and slightly incurved over the area, which 
has a height about equal to half the length of the valve. 
Dorsal valve moderately convex, a little inflected or concave towards the 
cardinal extremities; mesial fold broad, moderately elevated, rounded 
above and strongly defined : area linear. 
Surface marked on each side of the mesial fold and sinus by about four 
strong, low, rounded plications, .which are crossed by fine threadlike 
concentric striae and a few imbricating folds. Shell-structure punctate. 
A single specimen only of this species has been seen; but its great lateral ex¬ 
tension, comparatively low ai’ea, and few strong plications, preclude its union with 
any of the previously described species. 
The figures 11 & 12 of Plate xxvii are a dorsal and ventral view of this species. 
Geological formation and locality. In the Corniferous limestone, near Vienna, 
Ontario county. 
