172 PALAEONTOLOGY OF NEW YORK. 



Leiopteria Chemunuensis. 



PL \'i 1. \X1I. PIGS. 17, 18. 



Avicula Chemungenxis, Vim sbm. Geolog. Surv. N. V. : Rep. Third Dist., p. Inj. fig. 49, No. '■'•. 1842. 

 Leiopteria nitida, Hall. Pal. N. V.. vol. v, \>t. 1. Plates and Explanations: PI. 22, lij;s. 17. In, 



Jan., 1883. 



Shell of medium size or larger, rhomboid-ovate ; body elongate-ovate, oblique al 

 an angle of about 60° with the binge-line; length equal to more than four- 

 fifths of the height; anterior margin nearly vertical for about one-half 

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

 abruptly rounded. 



Left valve convex, gibbous in the umbonal region. Right valve smaller, 

 less gibbous. 



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



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

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



Mar of left valve small, bending slightly downward, defined by a broad 

 distinct sulcus ; extremity rounded. Ear of right valve flat, Byssal 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 stria 1 ; margin deeply concave in the middle; extremity 

 produced and acute. 



Surface, in a partial cast, marked by fine concentric stria?, which arc 

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

 appearing on the body as distinct undulations: these in the perfect' shell 

 may have been sharp lainelliform striae. 



Interior unknown. 



A specimen of the left valve has a length of 30 mm., height •">■"> mm., 

 hinge-line IV mm.; the body from beak to post-basal extremity measures 

 13 mm. 



The specimen figured is the original of Avicula Chemungensis, Vamxi.m. 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. 



