192 PALEONTOLOGY OF NEW YORK. 



LePTODESMA BlM,IN(iS[, 11. ^p. 



n.A IE i.xxxix. Ki(;s ij-i.-, 



SiiKi.i. larji't'. siili-rlioinhoidal ; lioily cloiigaty-ovatc, or sul)-r\ rniili-i<'al, \vv\ 

 oliliqiie; leiijitli alioiit twice the height; ante-by.ssal margin rounded, 

 heconiing (straight or slightly concave at the sinus; ventral margin hroadh- 

 (Hiving; posterior margin extended, acutely recurved at the i)Ost-l)asal 

 extremity. 



Let"t valve gihhous on tin' iiiuIk). convex lidow. Kiuiit salve ind\no\vn. 



Hinge-line straight ; length, including the spine, nearly (M|n,il to the length 

 of the valve. 



Beak sub-anterior, obtuse, slightly ol)li(iue, prominent, llmlxnial region 

 somewhat gibbous, subtending an acute angle. 



Anterior end limited by a slndlow byssal depression, acute and iiasute at 

 the extremity. Wing long, narrow-triangular, extending below the middle 

 of the valve; margin sinuate; extremity produced into a spine. 



Test thin, marked by line concentric stria' which aic alinipth arclu'd on 

 the posterior slope, regular upon the wing, and crowiled into line iiiegular 

 fascicles which are conspicuous on the anterior. Some speciineiis show sharp. 

 elevated, lamellose stria? at e([ual distances on the surface of the body. The 

 surface characters vary with the different states of cxfoliMtion iiiid maceration. 



The lArgest specimen observed has a greatest length, from beak to ba.^e, 

 of -u mm., height -iC) mm., hinge-line, to base of spine, >]•") mm. A small 

 example of the lel't valve has a length of o4 mm., height 1<S inni.. ami hinge- 

 line about :-»r> mm. 



This species is more elongate and oblique than L. longispinum, the wing extends 

 farther down along the posterior slope, and the anterior extremity is I'nlh r and 

 more acute. 



Formation and localities. In the (hemnng group at Panama, N. V. Other 

 specimens from near Elmira, >.'. Y., and Manslield, Tioga countx, Pa., are 

 referred to this species with reservation. 



