150 PAL.EOMX)JJJGY OF NEW YORK. 



Ptvchoi'teria louata, ii. !<p. 



fI-.\TK LXXXV, Vm. 37. 



Shell small. sul)-ilioinboidal ; bod}- broadly ovate, oblique at an angle of about 

 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 gil)bous; tlic point of greatest convexity is just below the 

 umbo. Right valve unkiuiw ii. 



Hinge-line straight, lengtli ncai-ly njual to the length of the valve. 



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

 forwanl. and arching over the nr.irgiu of the valve. Umbonal region ample, 

 gibbous, subtending an acute angle. 



Anterior end large, limited by a broad, undefined Iwssal depression ; 

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

 at the posterior end, strongly limited l)y 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 somewliat lamellose on 

 the anterior of the sbcll. 



Interior unknown. 



A left valve of this species has a length of lo mm., height 10 mm., binge- 

 line 1 1 mm. 



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

 stronger fold on tiic wing, wliiili is comparatively stronger than in any species 

 yet observed. 



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

 Warren county. Pa. 



