I 



LAMELLIBRANCHIATA. 367 



Umbonal slope rounded, with no defined limitation. There is a scarcely per- 

 ceptible flattening of the lower part of the shell from below the umbo to the 

 middle of the basal margin — a feature which is not always present. The 

 anterior end of the shell below the beak is marked by a shallow furrow with 

 a ridge on each side extending to the antero-basal margin. The posterior 

 ridge merges into the general convexity of the valve above. 



Surface marked by fine, closely arranged, concentric striae, which are some- 

 times crowded and fasciculate. The umbonal region and anterior end are 

 sometimes marked by strong, concentric folds. 



A specimen of this species has a length of 65 mm. and a height of 45 mm. 

 A larger individual has a length of 70 mm. 



In some of its phases this species resembles individuals of G. elliptica 

 which have the cincture scarcely developed, as in figs. 1 and 4 of plate Iviii, 

 but the broadly rounded posterior extremity of the present species, the sulcate 

 anterior end and constant absence of a cincture are distinguishing characters. 

 It also sometimes assumes the general form of G. drcularis, but in that species 

 the flattening of the shell and the constriction of the basal margin is posterior 

 to the middle, and it has no anterior fold or sinus. 



Formation and localities. In the arenaceous layers of the Hamilton group, in 

 Schoharie, Madison and Onondaga counties ; and in the soft shales of the group 

 on the shores of Skaneateles, Seneca and Cayuga lakes, and also near Bellona 

 and Moscow, N. Y. 



Grammysia bellatula. 



PLATE LXm, FIGS. 1-3. 



Cardimaorjjka bellatula, Hall. Prelim. Notice Lamellibranchiata, 2, p. 92. 1870. 



" " •' Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 63, figs. 1-3. 1883. 



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

 regularly curved without apparent constriction. Posterior extremity abruptly 

 rounded. Cardinal line straight, extending half the length of the shell. 

 Anterior end short, abruptly rounded below the lunule. 



"Valves regularly convex below and on the posterior end, becoming gib- 

 bous in the middle and umbonal region. 



