LAMELLIBRANCHIATA. 381 



Valves regularly convex toward the ventral margin, depressed-convex at 

 the posterior end and ventricose in the middle and above. 



Beaks at about the anterior third, large and prominent, incurving over 

 the hinge-line. Umbonal slope convex, gibbous above and gradually de- 

 clining into the general surface of the shell. Cardinal slope marked by one 

 or two inconspicuous folds. Cincture vertical, not strongly defined. 



Surface marked by fine concentric striae and by numerous concentric folds, 

 which are strong aud angular upon the anterior end, becoming regularly 

 bifurcated along the line of the cincture and thence continued to the 

 post-cardinal slope where they become rather abruptly obsolete. Interior 

 unknown. 



The specimen described has a length of 28 mm. and a height of 17 mm. 



This species is distinguished by the regular duplication of the concentric folds 

 along the cincture. It is more gibbous than either G. communis or G. Han- 

 nibalensis, more abruptly depressed at the posterior extremity, and distinctly 

 angular at the anterior end, a feature observed only in the first species here 

 cited. 



Formation and locality. In the upper beds of the Chemung group, at Warren, 



Pa. 



f 



Gbammysia Hannibalensis. 



PLATE LXI, FIGS. 29, 30, 33. 



AUorisiiia HaniiibalenxUi, Shumard. Geol. Surv. Missouri, Rep., pt. ii, p. 20(i, pi. c, tig-. 19. 1855. 



In part Grammysia Haimihalentds (Shumard), Hall, f relim. Notice Lamellibnmchiata, 2, p. 63. 1870. 



1 " " Mebk. Pal. Ohio, vol. ii, p. 300. PI. 10 ; tigs, 5a, b, c. 1875. 



., .. {Leptodcrmuxi) Hamubalensi.'i(iiii\iKKRD),Mki,i.. Pal. N. Y., vol. v, pt. 1. Plates and Ex- 



planations: PI. 61, tigs. 23-33. 1883. 



Shell below medium size, narrowly ovate or sub-elliptical ; length more than 

 one-third greater than the height; basal margin gently curved, more abruptly 

 curving at the anterior end, with a gentle sinus anterior to the middle. 

 Posterior extremity regularly rounded to about the middle of its height and 

 sub-truncate above. Cardinal line straight, extending more than half the 

 length of the shell. Anterior end abruptly rounded below the lunule. 

 49 



