382 PALEONTOLOGY OF NEW YORK. 



Valves regularly convex, becoming gibbous above the middle and in the 

 umbonal region. 



Beaks in advance of the anterior third, moderately elevated and incurved, 

 rising but little above the hinge. Umbonal slope rounded, not defined. A 

 broad gentle cincture extends from the beak to the ventral margin anterior 

 to the middle of the length. 



Surface marked by fine, closely arranged, fasciculate concentric striae, and 

 by stronger concentric folds, which are more distinctly developed in the 

 anterior and umbonal region. Frequently the concentric folds are very 

 irregular in their development, often bifurcating on the anterior part of the 

 valves and becoming obsolete before reaching the umbonal slope. 



Ligamental area narrow. Other characters of the interior unknown. 



Three specimens have lengths of 40 mm. each and heights of 25 mm. 

 Two smaller individuals measure respectively 33 and 38 mm. in length and 

 19 and 22 mm. in height. 



This species bears some resemblance to G. subarcuata, but is proportionally 

 more elongate and the concentric folds are much more strongly developed. 



Formations and localities. In the Waverly sandstones, at Summit and Cuya- 

 hoga Falls, 0., and in the Lithographic limestone at Hannibal, Mo. 



Grammysia plena, n. sp. 



PLATE LXI, FIGS. 31, 32. 



• 

 In part Grammy»ia Hannibal ai/ris (Shimaud), Hall. Pi-elim. Notieo Laiiiellibranchiata, 2, p. 62. 1870. 



" " (Leptodomusf) Haimilialtn^is (fyHV.MAHD),UALh. Pal. N.Y., vol. v, pt. 1. Plates and Kx- 



planations: PI. 61, fife'.s. 23-33. 1883. 



Not AUnr'unaa HannihaleTixis, Shumard. Geol. Surv. Missoui-i, Rep., pt. ii, p. 206, pi. c, fig. 19. 1855. 



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

 height ; l)asal margin regularly curved from the post-basal extremity, except- 

 ing a gentle constriction, or sinus, at about the anterior third. Posterior 

 extremity obliquely truncate above. Cardinal line straight, more than half 

 the length of the shell. Anterior end short, abruptly rounded below the 

 lunule. Lunule deep and distinct, extending more than half way from the 

 beak to the base of the shell. 



