478 PALEONTOLOGY OF NEW YORK. 



upon the body of the shell, more distant on the anterior end, and finer and 

 more closely arranged on the post-cardinal slope. 



Two specimens measure respectively 18 and 23 mm. in length, and 8 and 

 9.5 mm. in height iit the posterior extremity. 



In its surface characters this species is more nearly related to P. sedifrons, 

 but it is more symmetrically elliptical, more convex, the beaks more incurved 

 and there is no fold on the post-cardinal slope. 



Formation and localities. In a shale of the Chemung group, near the level of 

 the Alleghany river, at Warren, Pa., associated with Echinocaris socialis and 

 other Phyllocarida. 



ORTHONOTA, Conrad. 1841, 

 Orthonota undulata. 



PLATE LXXVIII, KIGS. 37-42. 



Orihtmota undtUcUa, Cohbad. Geol. Surv. N. Y., Ann. Rep., p. 51, pi., fig. 6. 1841. 



" " Vakuxkm. Geol. Surv. N. Y., Rep. Third Dist., p. UO, fifj. 2. 1842. 



" " " Hall. Pi-elim. Notice Lamellibranchiata, 2, p. 87. 1870. 



" " " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI 78, figs. 



37-42. 1883. 



Shell large, extremely elongate, with parallel dorsal and ventral margins ; 

 length three times the greatest height ; basal margin nearly straight, slightly 

 constricted anterior to the middle. Posterior end somewhat vertically trun- 

 cate. Cardinal line straight, extending for about three-fourths the length of 

 the shell. Anterior end short, extending for a little distance along the hinge- 

 line and abruptly rounded. 



Valves of moderate convexity. 



Beaks sub-anterior, small, low, scarcely elevated above the hinge-line. 

 Cincture narrow, distinct, extending from the beak to the basal margin, 

 which is sometimes gently constricted. Umbonal ridge prominent, rounded, 

 limited below by a narrow furrow, and extending to the post-inferior extrem- 

 ity. Cardinal slope wide, marked by a distinct fold along the middle of its 

 length. 



