LAMELLIBRANCHIATA. 373 



Grammysia zonata. 



PLATE LXIII, FIGS. 4, 5. 



Cardiomorpha zonata. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 63, fig. 5. 1883. 

 Cardwnwrpha cmicentrica. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations ; PI. 63, fig. 4. 1883. 



Shell small, ovate-elliptical ; length one-third greater than the height ; basal 

 margin regularly curving into the anterior and posterior margins Avithout 

 evidence of constriction. Cardinal line nearly straight, slightly declining 

 backward. Anterior end short, abruptly rounded. 



Valves moderately convex in the lower and posterior portions, and gibbous 

 in the middle and umbonal region. 



Beaks at about the anterior third, directed forward and incurved. Umbo- 

 nal slope sub-angular above, merging into the general convexity of the shell 

 below. Post-cardinal slope limited below by a strong fold, with a narrow 

 plication between it and the cardinal margin. 



Surface marked by fine concentric striae and strong concentric ridges, 

 which are continuous to the post-cardinal slope. Interior unknown. 



The two specimens described measure respectively 13 and 20 mm. in 

 length, and 8.5 and 13 mm. in height. 



This species differs from G. bellatula in its more elliptical outline, the strong 

 continuous concentric undulations of the surface and the cardinal .slope marked 

 by two distinct longitudinal folds. 



Formation and locality. In the Hamilton group, near Summit, Schoharie 

 county, N. Y. 



Grammysia arcuata. 



PLATE LXI, FIGS. 1-9; PLATE LXIU, FIG. 6? ; and PLATE XCIII, FIG. 37. 



Poiidtmiat arcuata, CosvikD. Geol. Sui-v. N. Y., Ann. Rep., p. 03. 1841. 



Orammysia arcuata (Conrad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 56. 1870. 



" (Leptodomus) arcuata (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 



PI. 61, figs. 1-9. 1883. 



" donorf/onnw. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 63, fig. 6. 1883. 



Shell of medium size, ovate ; length about one-third greater than the height ; 

 basal margin moderately curved, straight or slightly concave along the middle. 

 48 



