9G PALEONTOLOGY OF NEW YORK. 



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

 preserved specimen from the Corniferous limestone, at Staflford, 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 abuiidaiit in the Hamilton group at numerous localities 

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

 thougli occuning at Hamburg and elsewhere on Lake Erie shore. It is found 

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

 county, Pennsylvania. 



Ptkrtnka intkrstrtaup, n. sp. 

 rr.ATE i.xxxiv. fh; ■.■■.>. 



Shell large: lel't valve (ihliijiiely 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 straiglit, about equal to tiie length of the shell. 



Beak acute, inclined forward. Um})onal region not prominent, narrow, 

 limited hy 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 : w itli 

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

 crossed by fine concentric stria\ Al)out 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. Tiie wing shows tlie radii somewhat less 

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



Interior uid<nown. 



The specimen described has a greatest length ol' aliout "io mm.; height 

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



