172 PALjEONTOLOGY OF NEW YORK. 



Leiopteria Chemungensis. 



PLATE XXII, FIOS. 17, 18. 



Apicula Vhemiingeiisis. Vani xkm. (xcdldfr. Surv. N. V. : Rei>. 'I'liinl Dist., p. 182, tig. 40, Nn. 'i. 1842. 

 fyeiiipteria uitida. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 22, lig«. 17, 18. 



Jan., 1883. 



SiiKLL ut iiic'diiuii !<i/A' ur larger, rhomboid-ovate : bod}- elongate-ovate, oblique at 

 an angle of about 00° with the hinge-line; length equal to more than fi)ur- 

 fit'th.s of the height; anterior margin nearly vertical for about one-hull' 

 the height of the shell and broadly rounded on the base ; post-basal margin 

 abruptly rounded. 



Left valve convex, gibbous in tlie umlM)nal region. Kiglit valve smaller, 

 less gibbous. 



Hinge-line straight, a little longer tlian tlie height of the shell. 



Beaks sub-anterior, inclined forward, acute, prominent, arching over the 

 hinge. Umbonal region narrow, prominent, subtending an acute angle. 



Ear of left valve small, Ijending slightly downward, defined by a broad 

 distinct sulcus ; extremity rounded. Ear of right valve flat. B3^ssal sinus 

 shallow and broad, deeper in the right valve. Wing broad-triangular, 

 joining the body below the middle of the length, limited by the abrupt 

 bending of the striae ; margin deeply concave in the middk' ; extremity 

 produced and acute. 



Surface, in a partial cast, marked by fine concentric striae, which are 

 crowded and lamellose on the ear, distinctly marked on the wings, and 

 appearing on the I)ody as distinct undulations: these in tlie perfect shell 

 may have been sharp lamelliform striae. 



Interior unknown. 



A specimen of the left valve has a length of 30 mm., lieight •"!;") mm.. 

 hinge-line 47 mm.; the body from beak to post-basal extremity iiiea,siu-es 

 43 mm. 



The specimen figured is the original of Avicula Chemungensis, Vanuxkm. It 

 resembles L. Dekayi of the Hamilton group, but differs in its longer hinge-line, 

 larger wing, and more acute beak, while the body of the shell is narrower. 



