330 PALEONTOLOGY OF NEW YORK. 



tion, becoming straight toward the posterior. Posterior extremity abruptly 

 acute, not attenuate. Cardinal line straight, oblique. Anterior end large, 

 broadly rounded, comprising half the shell. 



Valves convex, very gibbous in the anterior portion and in the umbonal 

 region. 



Beaks behind the anterior third, prominent, rising above the hinge-line. 

 Umbonal ridge defined, angular, curving downward, abruptly sloping to the 

 posterior extremity. 



Surface marked by fine, even, concentric striae, which are obsolete on the 

 post-cardinal slope. Interior unknown. 



Two specimens measure respectively 9 and 11 mm. in length, and 6 and 7 

 mm. in height. 



This species differs from L. rostellata in the shorter and less curved posterior 

 end ; the anterior portion is broader and more extended ; the beaks are more 

 distant from the anterior extremity. 



Formation and localities. In the shaly sandstones of the Hamilton group, from 

 near Summit and Jeflferson, Schoharie county, N. Y. 



Leda rostellata. 



PLATE XLVU, FIGS. 42-47. 



NuculUes rostellata, Cokrad. Geol. Surv. N. Y., Ann. Rep., p. 50. 1841. 

 Ledat rostellata (Conrad), Hall. Pi-elim. Notice LanielliViranchiata, 2, p. 5. 1870. 

 Leda (Nucidana) rostellata (Conbad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 47, 



figs. 45-47. 1883. 

 " " perstriata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations ; PI. 47, figs. 



42-44. 1883. 



Shell small, falciform; length more than twice the height; basal margin 

 gently curving from the posterior extremity, more rapidly curving anteriorly. 

 Posterior end attenuate, arching upward, with the extremity narrowly 

 rounded or sub-truncate. Cardinal line oblique, declining posteriorly, and 

 regularly curved. Anterior end comparatively short, abruptly rounded. 



Valves convex, somewhat gibbous in the umbonal region, depressed-convex 

 posteriorly. 



