162 PALAEONTOLOGY OF NEW YORK. 



sions: length 39, 34, and 25 mm., height 41, 38, and 26 mm., hinge-line 37, 

 39, and 20 mm. The right valve, mentioned above, is 23 mm. in length, 25 

 mm. in height, and 23 mm. along the hinge-line. 



This species re.sembles the two preceding, but the form of body is more 

 narrowlv ovate, the oliliquity appears to be intermediate between the two; 

 the i-ar is less strongly defined : tlic wing is comparatively narrower, and less 

 extended at the extremity. 



Formation and localities. In the shales of the Hamilton group, on the shores 

 at Skaneateles lake ; at Bellona, Yates county, and Leonardsville, Madison 

 county, N. Y. ; a single specimen from the Corniferous limestone of Delaware, 

 Ohio, has been referred to this species. 



Leiopteria S.\yi, n. sp. 



Pr.ATK I.XX.WUI, FIGS. 1.5-20. 



Shkll above the medium size, sub-orbicular ; body very broadly ovate, scarcely 

 oblique; height greater tlian tlu' length; margin nearly straight in front. 

 thence regularly rounded. 



Left valve very convex, gibboiis in the umbonal region. Right valve 

 smaller and less convex. 



Hinge-line straight, longer tlian the length of the slicll. 



Beaks acute, situated near the anterior extremity of the hinge, i)roniiiient, 

 inclineil lorwnrd, ar<liing over the hinge-line. Umbonal region ample, sub- 

 tending a right angle. 



Kar small. Iicuding downward, flclincd by a broad, shallow sulcus. i?yssal 

 sinus narrow. Wing large, triangular, greatly extended along the hiiigc-linc, 

 defined by the retral bending of the stria^; margin concnve; extremity acute. 

 The wing of the right valve is very broad. Hat. and iiuirh extended : not ilis- 

 tinctly defined. 



Surface marked by fine, clo.sely arrangeil stria^ of growtli, with distant, 

 elevated lamelhe, which are extensions of strong i'a.scicli's of stria'. These 

 leave angular concentric folds and undulations in the casts. The stria' are 



