hes Se OSTRACODA. 647 
cinnati specimens. The surface also is scarcely so convex, or rather it is not thrown 
up into a point near the center, but is comparatively uniform in curvature. 
Aparchites tyrrellii Jones (Contri. Can. Micro-Pal., pt. 111, p. 62; 1891) from the 
Chazy at Lake Winnipeg, is a closely related, if not identical form. However, as 
figured by Prof. Jones, it appears to be less convex and the outline not so prominent 
in the post-ventral region. 
Formation and locality.—The small specimen is from the middle third cf the Trenton shales near 
Fountain, the larger from the top of the Galena shales near Cannon Falls, Minnesota. 
Family BEYRICHIID A. 
Genus PRIMITIELLA, n. gen. 
Carapace usually oblong, equivalved, moderately convex; surface smooth or 
finely punctate; in the dorsal slope a broad, shallow and quite undefined depression 
represents an undeveloped mesial sulcus. : 
Type: LP. constricta, n. sp. 
Besides the four new species about to be described, I propose to place in this 
genus Leperditia unicornis Ulrich (Aparchites, Ulrich, Primitia, Jones) and Primitia 
whitfieldi Jones, from the lower part of the Cincinnati group, Primitia ulrichi Jones, 
Utica slate, Canada, and probably the European species, Primitia matutina and bey- 
- richiana Jones and Holl, Primitia minuta Hichwald (as figured by Jones) and 
P. elongata, var. nuda, Jones. I am inclined to think that Isochilina? fabacea Jones, 
from the Hamilton of New York, and Aparchites inornatus Ulrich also should be 
placed here. These species constitute a very natural group, distinguished from 
- Aparchites by the dorsal depression. -They are separated from Primitia because they 
give no adequate idea of that most prolific genus. To be a Primitia in my eyes the 
_ valves must be provided with a well marked subcentral pit or sulcus. 
The Carboniferous genus Youngia, Jones and Kirkby, is closely simulated in all 
respects except the crenulated hinge by Primitiella limbata. Possibly that genus is 
not so far removed from Primitiella as we now believe to be the case. 
- PRIMITIELLA CONSTRICTA, 1”. Sp. 
PLATE XLII, FIGS. 48—52. 
Sizz.—(E. C.) Kentucky specimen: Length 0.67 mm.; hight 0.36 mm.; thickness 0.24 mm. 
Minnesota igen ORGO A Ne O35) CLNatiae (Ose Ly 
“ ss ti 0.68 sce Oedda ¢ OS Ope, 
Carapace elongate, subelliptical or subquadrate, the length nearly twice the 
hight, convex; dorsal margin long, straight, with both extremities angular, or with 
the anterior one obtuse or rounded; ventral margin nearly parallel with the dorsal, 
