ir,4 PALJEONTOLOGY OF NEW YORK. 



Lkiopteria Dekayi. 



I'l.ATE XIX. KIG 1 ; I'LATK .\.\, FICJS. HV18 ; and PLATE LXXXVIII, KIGS. 5-10. 



r^ii>})terii( Dikiuji. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 19, fig-. 1 ; pi. 20, figs. 



lU-lS. (lit in error). Jan., 18S3. 



Shell oi" medium size, sub-rhomboidal in general form ; body narrowly ovate, 

 oblique; length about equal to tlH> lioiglit; anterior margin nearh- vertical 

 lor one-third the length of the .shell, thence broadly rounded over the ba.sal 

 margin and abruptly recurved at the post-basal extremity. 



Left valve convex, gibbous on the umbo. Right valve smaller and less 

 convex; the limitation of tlic wing not strongly defined. 



Hinge-line straight, length a little less than the lengtli of the .-^licll 

 measured from the anterior side of tlic beak to the cxtrcuiity of the wing. 



Beaks anterior, acute, pi'ominent, inclined forward. Umboual region 

 gibbous above, regularly convex below, subtending an acute angle. 



Ear l)ending downward, with a strong fold in the upper part, limited bv 

 a broad undefined sulcus and shallow byssal sinus. Wing triangular, tiat, 

 defined Ijy the abrupt retral Ijending of the stria3 and a depressed line along 

 the post-cardinal slope ; margin concave ; extremity acute. 



Test thin, marked by fine regular concentric strijv, which at unequal 

 intervals arecrowdeil into fascicles, giving an uiKhilatt'd as])e('t to the surface 

 of the cast ; in old specimens, more crowded on the anterior side and ear, 

 and on the wing usually regular, sometimes becoming a little fosciculate on 

 the margin. 



This description of the surface is taken from casts or partial casts which 

 preserve more or less the surface markings. In a few ^-ounger specimens 

 from the shales, the surface shows tine regular stria' which gradually l)ecome 

 fasciculate as the shell increases in size. 



Ligamental area narrow, marked by fine stri;e ; helow this area is a narrow 

 oblique fold or lateral tooth. 



The three specimens figured on plate xx, have respecti\ely the following 

 dimensions : length 37, 31, and 20 mm., height 37, 3(1. and 3(1 mm., hinge- 



