96 PALMONTOLOGY OF NEW YORK. 



Formations and localities. This species has been recognized in a single ill- 

 preserved specimen from the Corniferous limestone, at Stafford, Genesee county, 

 N. Y. ; casts of the interior, and a single extravagant form preserving the sur- 

 face characters, have been obtained from limestone of the same age near Col- 

 umbus, Ohio. It is abundant in the Hamilton group at numerous localities 

 from Schoharie to Cayuga lake, more rarely in the western part of the State ; 

 though occurring at Hamburg and elsewhere on Lake Erie shore. It is found 

 in the upper beds of the Chemung group in Steuben county, N. Y., and Tioga 

 county. Pennsylvania. 



Pterinea interstrialis, n. sp. 



PLATE I. XXXIV, PIG 23. 



Shell large; left valve obliquely ovate, narrow above; length and height 

 nearly equal ; anterior and basal margins regularly curved ; posterior margin 

 produced. 



Left valve moderately convex, depressed towards base. Right valve 

 unknown. 



Hinge-line straight, about equal to the length of the shell. 



Beak acute, inclined forward. Umbonal region not prominent, narrow, 

 limited by the cardinal expansions ; subtending an acute angle. 



Wing triangular, large ; margin concave ; extremity acute. Ear triangular, 

 small. 



Surface marked by about 20 regular, strong, rounded rays which originate 

 on the upper part of the umbo and continue undivided to the margin; with 

 broad, flat interspaces marked by from two to four slender, sharp radii, and 

 crossed by line concentric stria?. About twelve of the strong rays reach the 

 margin of the valve below the middle of its height, the remainder come out 

 on the upper anterior margin. The wing shows the radii somewhat less 

 strong than the body of the valve. The ear is marked by strong radii. 



Interior unknown. 



The specimen described has a greatest length of about 5-5 mm.; height 

 Dearly 58 nun.; hinge-line from beak to extremity of wing, about 58 mm. 



