ORDOVICIAN FAUNAS. 169 
WHITELLA SUBTRUNCATA (Hall). 
Plate XI., Fig. 4. 
1847. Hdmondia subtruncata Hall, Pal. N. Y., vol. I., p. 156, pl. 
35, figs. 3 a—b (not fig. 3c, or pl. 34, fig. 9). 
Description.—Shell oblique, elongate, ventricose, subelliptical in 
outline. Beaks small, prominent, strongly incurved; umbones promi- 
nent, projecting beyond the hinge-line. Anterior extremity of the 
shell rather sharply rounded, the antero-basal margin gently convex 
or nearly straight, the posterior extremity broadly rounded, the 
postero-dorsal margin convex, rounding into the posterior extremity 
of the arcuate hinge-lne. Umbonal ridge arcuate, sharply angular 
near the beak, becoming more and more broadly rounded as it ap- 
proaches the postero-basal extremity of the shell. The post-umbonal 
slope abrupt, concave; the anterior slope convex. 
The dimensions of a nearly-perfect right valve are: length from 
beak to postero-basal extremity, 37 mm.; width at right angles to 
last dimension, 25 mm.; convexity, 11 mm. 
Remarks.—The several specimens illustrated by Hall to represent 
Edmondia subtruncata undoubtedly belong to more than one species 
and probably to two or more genera. The New Jersey shell which 
is referred to this species is somewhat common in some of the higher 
Trenton beds in the Jacksonburg section, and is believed to be spe- 
cifically identical with Hall’s specimen illustrated by figure 3a. Fig- 
ure 3 b may also be the same, but the other specimens illustrated are 
distinct. The New Jersey specimens are evidently members of the 
genus Whitella, and the species is here transferred to that genus. 
MODIOLOPSIS FABA (Con.). 
Plate XI., Figs. 13—15. 
1847. Modiolopsis faba Hall, Pal. N. Y., vol. L., p. 158, pl. 35, figs. 
6 a-c. 
Description.—Shell small, about twice as long as high, the greatest 
height in the posterior half; the beak situated about one-fifth the 
length of the shell from the anterior extremity, somewhat compressed 
