
134 Cincinnati Society of Naturat Firstory. 
PRIMITIA GLABRA, 0. Sp. 
Plate X, Figs. 9a, 96 and ge. 
Carapace comparatively large, moderately convex, the point of 
greatest convexity about the center of the posterior half. Hinge 
edge straight; anterior end semi-circular ; posterior end somewhat 
oblique, very gently curved in the lower half, more abruptly in 
the upper; ventral edge gently convex; free margins with a mod- 
erate flange, widest at the ventral and posterior margins. Mesial 
sulcus represented by a broad, illy-defined and very shallow 
depression in the dorsal slope. Surface smooth. 
Size: Length, 1.9 mm.; height, 1.17 mm,; greatest convexity 
of single valve, 0.45 mm. 
This fine species belongs to a group of forms that approach /so- 
chilina, the characteristic median sulcus of Primitia being almost 
obsolete. /. valida, J. and H., from the Wenlock of England, is 
another member of this group, and appears to be closely related to 
P. glabra, but differs in having a punctate shell, centrally restricted 
mesial depression, and the point of greatest convexity nearer the 
ventral edge. Of American species the Chazy group P. loganz, 
Jones, may be compared. The dorsal notch in that species is, 
however, deeper, the shape of the carapace slightly different and 
the shell usually punctate. The outline of the anterior half in a 
ventral view, also shows the anterior slope to be more abrupt. 
Position and locality: Upper beds of the Cincinnati Group, at 
Oxford and Blanchester, O. The species seems to be rare. 
PRIMITIA NODOSA, N. Sp. 
Flate X, Figs. 11a, 116, 12a and 120. 
This is a very neatly punctate species, having a straight dorsal 
margin, sub-equal ends, and nearly uniformly rounded ventral 
edge, with a distinct flange all around the free margins. ‘There is 
no true sulcus; but the interval between two strong, rounded 
nodes situated one on each side of the center of the dorsal edge 
and projecting slightly beyond it, may represent the generic notch 
or sulcus. ‘The anterior one of these knobs is the larger. A third 
node, smaller than either of those at the dorsal margin, occurs 
near the posterior edge, while a fourth rather inconspicuous eleva- 

