108 
PALEONTOLOGY OF NEW-YORK. 
appear to be subject to such extreme variations in respect to the striae. It resem¬ 
bles very closely, in its surface markings, the S. textilis, but is always smaller, with 
a more extended hinge-line, and never so flat as that species. In the same respects 
it is not very dissimilar to some of the other species of the Upper Helderberg and 
Hamilton groups ; and it has been confounded with S. inequiradiata, which is a 
much larger shell, with different internal characters. Its surface striae are more 
delicate than any of the other species, and its muscular impressions are peculiar 
in form and details, and entirely unlike those of any other species, as shown in 
figures 2 h, i, k, on Plate xvin. 
The general characters of the species and varieties* of form are shown in figures 
2 a-k, on Plate xvm. 
After critical comparison of all the other species of the Hamilton group, I am 
convinced that the species of Mr. Conrad is the one I have here described and 
illustrated, although not entirely corresponding with the original description. 
Geological formations and localities. This species occurs in the Corniferous lime¬ 
stone somewhat^ rarely, but is common in the Hamilton group, and is at present 
unknown in any higher position. It is common in localities along the shores of 
Seneca, Cayuga and Canandaigua lakes; at Moscow; York; Pavilion; Darien; 
Eighteen-mile creek, and numerous other places in the Hamilton group. Its locali¬ 
ties in the Corniferous limestone have already been enumerated on page 88. 
Strophodonta textilis. 
PLATE XVIII. 
Strophomena ( Strophodonta ) textilis : Halx., in Tenth Report on State Cabinet, p. 141. 1847.. 
Shell very thin, nearly flat, transverse, semioval, sometimes nearly as 
long as wide, the length being from two-thirds to four-fifths the width; 
hinge-line equalling or sometimes a little greater than the width of 
the shell below, with salient angles. 
Ventral valve slightly convex. Dorsal valve gently concave. 
Area of the ventral valve narrow, almost linear, and extremely narrow 
towards the extremities, vertically striated, with a narrow callosity in 
the centre; the inner margin crenulate for about two-thirds its length. 
Area of the dorsal valve linear, scarcely half as wide in the middle as 
that of the opposite valve. 
