839 



Ptycho. 



turning abruptly outward just below the hinge, and becoming 



24/ Vlilj. 



Ylllg 



lamellose on front part of valve. Randall's collections at War- 

 ren, Pa. Specimens 9614, 9615, 9619 ; wrongly labelled Allo- 

 risma. VIII g. 



Ptychopteria mesocostalis, H. S. Williams. U. S. Geolog- 

 ical Survey, Bull. No. 41, 1887, 

 pages 35, 36, plate 3, fig. 9, en- 

 larged twice^ doubtful genus, 

 in Portage shales at Warsaw, N. 



Y. ; fig. 12, enlarged twice^ left valve, variety, from same at 



Attica, N. Y. VIII f, 



Ptychopteria obsoleta, new species Simpson. Trans. Amer. 



Phil. So. Philada , 1889, page 448, fig. 15. 

 '"^""'WHPk Species based on Randall's specimen 9622, 

 U, y . wrongly labelled Yoldia. Shell of medium 

 size, subrhomboidal in outline ; body ovate 

 oblique, at an angle of about forty degrees 

 APS Tr. 1889 to the Mugo line ; height about three-fourths 



the length. Anterior margin abruptly rounded ; basis margin 

 curved outward at the extremities, concave at the middle ; pos- 

 terior margin somewhat abruptly recurved. Right valve un- 

 known. Left valve moderately convex ; greatest convexity at 

 the umbonal regions. Hinge line essentially straight; length 

 a little less than that of the body. Beak situated at about the 

 anterior fourth of the shell, small, extending beyond the hinge 

 line. A shallow broad sinus extends from the beak to the 

 basal margin a little anterior to the middle. Anterior extrem- 

 ity acuminate, margin rounded. Wing triangular, joining the 

 body at the posterior extremity; margin for a short distance 

 straight, then abruptly curving forward, and just before reach- 

 ing the cardinal line curving upward. Wing convex; flattened 

 26 



