482 PALEONTOLOGY OF NEW YORK 



OrTHONOTA (?) PARVULA. 

 PLATE LXV, FIOS. •-', 3 ; AND IM.ATK LXXVIII, FIGS. S9-32. 



OrUionota parvula, Haix. Pi-elim. Notice Lamellibruiichiata, 2, p. 88. 1870. 



" " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 78, figs. 29-32. 1883. 



In jMU-t Sangu'molites truH<.-attui (Cokkad, sp.), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 



PI. 65, figs. 1-15. 1883. 



Shell small, elongate, sub-trapezoidal ; length three times the height. Ventral 

 and dorsal margins straight and sub-parallel. Posterior extremity vertically 

 or obliquely truncate below and curving forward above. Anterior end nar- 

 rowly and regularly rounded from the "cardinal margin. 



Valves moderately convex below and posteriorly, becoming gibbous in the 

 middle and umbonal regions. 



Beaks at about the anterior fourth, flattened and incurved, rising very little 

 above the hinge-line. Umbonal slope angular, extending to the post-inferior 

 extremity. Post-cardinal slope Hat or slightly concave, sometimes obscurely 

 marked by a depression or fold below the middle. 



Surface marked by extremely fine, thread-like concentric striaa, which are 

 often lamellose on the post-cardinal slope. 



Three specimens measure respectively 14, 15 and 20 mm. in length, and 

 4.5, 5 and 6 mm. in height. 



This shell was placed under the genus Orthonota on account of its long, 

 straight hinge-line and absence of a lunule and any indication of external liga- 

 ment. The two valves are frequently in conjunction as in other species of 

 Orthonota. The surface markings are in no respect like 0. undulata, but do not 

 differ essentially from 0. carinata. Its generic relations are still in doubt. 



Formation and localities. In the shales of the Hamilton group near Fulton- 

 ham and Summit, Schoharie county ; in Onondaga and Livingston counties ; 

 and on the shores of Seneca and Canandaigua lakes, N. Y. 



