144 PALAEONTOLOGY OF NEW YORK. 



t\w liinitinj:' fminw distinct; tiif ioM unitU' and the upprr jiart of tlir wiiiff 

 tint or sli<ilitly cuiivcx ; iiiariiiii <iliiii|iicl\ tiimcatt', concave jnst hclow tlic 

 hinge; extremity slightly produccii. 



Sini'acc marked 1)\- fine nnit'onn radii on the hoily and w inn', whicli arc 

 nearh ohsolctc on the anterior end, and sometimes interrupted on the hody 

 hv varices of growth ; also liy line concentric stria; which are acutely 

 recur\i'd o\'er the ant:nl,ir posterini- slope ol' tlie hody, and crowiled into 

 fiiscicles at ii'ret:iihir inler\als, ])io(hicing an umhihited apjiearance. 



Interior unknown. 



A lar^e left valve has a length of ')'! mm., height "JS mm., and hinge-line 

 3(j mm. .\ rii:ht \al\c in the same association has a length of in nnii., 

 height -!<• mm., and himie-liue '.',:] mm. 



This s])ecies somew lial reseniiiles P. Irigonalis, hut the postei'ioi' extremity is 

 more produced, and the wing more ohliijuely tianicate on the nnu'gin. The 

 right \alve in general aspect resemhles the right valve ol' /-". alala. hut the left 

 valve is very dissimilar. The distinguishing characters are its large rhomhoidal 

 form, extreme gihhosity and ai-cuation of the left valve. 



Formation and locality. In a compact sandstone of the Upper Chemung group, 

 in the lower l)eds as seen at Wairen, Pa. 



PtYCIIOPTERIA SP.VTILATA, U. Sp. 

 1M..\TE I.X.WV. KIC. 20. 



Shell large, elongate, rhondioidal : l)ody snh-elliptical. ohli(pie at an aniile of 

 ahout ;')0'^ with the hinge: length more than one-third greater than the 

 height; ante-hyssal mamin ol)li(pie. gently curving into the simis, thence 

 extending into the hroadly curvi'd hasal margin ; posterior end rectangularly 

 or acutely recurved. 



Left valve moderately convex, slightly gihhous above. Ilighl valve 

 depre.ssed-convex, more snh-angular along the post-cardinal slope, and smaller 

 than the left. 



