L50 PALEONTOLOGY OF NEW YORK. 



Ptychoptbwa LOBATA, 11. sp. 



PLATE L.WXY, IK. 87. 



Shell small, sub-rhomboidal ; body broadly ovate, oblique at an angle of aboul 

 55° with the cardinal line; length somewhat greater than the height; anterior 

 margin sub-truncate; base broadly rounded; posterior margin rectangularly 

 recurved into the wing. 



Left valve very gibbous; the point of greatest convexity is just below the 

 umbo. Righl valve unknown. 



Hinge-line straight, length nearly equal to the length of the valve. 



Beak situated anterior to the middle of the hinge, prominent, inclined 

 forward, and arching over the margin of the valve. Umbonal region ample. 

 gibbous, subtending an acute angle. 



Anterior n\<\ Large, limited by a broad, undefined byssal depression; 

 margin convex; extremity apparently obtuse. Wing small, joining the body 

 at the posterior end, strongly limited by a deep furrow and very marked 

 alar plication; margin nearly straight; extremity angular. 



Surface marked by fine radiating striae which become finer on the wing 

 and anterior end: and by striae of growth which are somewhat lamellose on 

 the anterior of the shell. 



Interior unknown. 



A left valve of this species has a length of 13 mm., height 10 nun., hinge- 

 line 11 nun. 



This species differs from P. gibbosa in its shorter, truncate anterior end. and 

 stronger fold on the wing, which is comparatively stronger than in any species 

 yet observed. 



Formation and locality. In the sandstones of the Upper Chemung group. 

 Warren county. Pa. 



