32 PALJEONTOLOGY OF NEW YORK. 



tlircctfd sli-ilitly IVnwaid, depressed. Umbonal region moderately prominent, 

 subtending an angle a little less than 90°. 



Ears triangular, flat, extremities jicut«. Anterior ear smaller, ilefined by 

 a sulcus ; margin nearly straight. Posterior ear with the margin concave, 

 extremity aciiiniiiatr : having no strong radiating striae. 



Test, as indicated in an exfoliated specimen, marked by a few fine radiating 

 stria\ with wider interspaces whieli are marked by finer radii. Anterior 

 ear sliuwing the same eliaracters. Posterior ear I'ree from rays. Fine 0(m- 

 centric stria> cross the rays, ami stronger concentric wrinkles interrupt them 

 and proihice a slight crenulation of the radii. 



The specimen is Id.-') nun. in length, 10 nun. in lieight, with hinge-line a 

 little more than 1 1 mm. 



This .species resenil)les in tbrm the young ol' Pterinopeden dignatus, but differs 

 in the liner radiating lines on the liody of the sliell, the concave margin, and 

 absence of rays on the })osterior ear. 



Formation and locality. In tbe black Marcellus shale at Cherry Valley, Otsego 

 county, N. Y. 



AVICULOPECTEN (PtERINOPECTE.X ?) TEKMINWLIS. 



PLATE I, FIO. 3. 



Plerint)ptctenterminalis.U\u,. Pal. N. Y., vol. v, jit. 1. Plates and Kxplaimtidii.-s : PI. l.fiy. 3. Jan., 18S3. 



iSliKi.i, small, rliomlioidal : hody of the sliell obli(piely ovate; length a little 

 greater than the height ; margins regularly rounded, somewhat extemled 

 lichind. 



hfft valve very convex. Kiglit valvi' unknown. 



Hinge-line straight, central, eipial to the length of tlu' sludl. 



Heak acute, prominent, directed a little forward, arching over the hinge- 

 line. Uml)o elevated, sul)teudiug a right angle. 



Ears triangulai-; margins concave; extremities acute. Posterior ear larger, 

 iindefnied. Anterior ear limited 1)V a shallow sidcns. TJvssal sinus moderate. 



