LAMELLIB RANCHI A TA. 
291 
Yalves moderately convex in the posterior part, gibbous in the middle and 
umbonal region. 
Hinge-line short, oblique, about one-third the length of the shell. 
Beaks anterior, prominent, small, distinct. Umbonal slope rounded, flat¬ 
tened on the anterior side. 
Test thin, marked by fine concentric striae. Interior unknown. 
The specimen described has a length of 24 mm., and a height of 15 mm. 
This form is distinguished from M. subalata, var. Chemungensis, by the absence 
of defined umbonal ridge, and in the regularly rounded posterior extremity. 
Formation and locality. In the Chemung group, Buck’s quarry, near Elmira, 
N. Y., associated with Orthis impressa, Atrypa hystrix, and Produdella, Boydi. 
Modiomorpha Tioga, n. sp. 
PLATE XL, FIG. 18. 
Modiomoi'phct? amygdalina (Winchell, sp ), Hall. Prelim. Notice Lamellibranchiata, 2, p. 78. 1S70. 
In part “ “ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 
PI. 40, figs. 15-19. 1883. 
Not Sanguinolites amygdalinus, Winchell. Proc. Acad. Nat. Sci. Phila , p. 13. 1S63. 
Shell of medium size, sub-ovate, wider behind, sub-truncate at both extrem¬ 
ities ; length one-half greater than the height; basal margin slightly sinuate 
in the middle, curving toward the extremities, and abruptly rounded into 
the anterior and posterior margins. Posterior margin sub-truncate in the 
upper portion. Anterior end declining abruptly from the beak and narrowly 
rounded in front, limited by an obscure depression extending from the beak 
to the basal margin. 
Valves depressed-convex posteriorly and in the lower part, moderately 
convex in the umbonal region. 
Hinge-line imperfect in the specimen described. 
Beaks situated a little less than about one-fourth the length of the shell 
from the anterior end, small, closely appressed, rising very little above 
the hinge. 
Test thin, marked by fine concentric striae, which, in some parts, have 
