OSTEACODA.. 647 



Prlmltlella.]. 



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. iii, 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 tocaZitj/.— The small specimen is from the middle third of the Trenton shales near 

 Fountain, the larger from the top of the Galena shales near Cannon Falls, Minnesota. 



Family BEYRICHIIDJE. 

 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: P. 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 Eichwald (as figured by Jones) and 

 P. elongata, var. nuda, Jones. I am inclined to think that Isochilina ? fahacea 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 hy Primitiella limhata. Possibly that genus is 

 not so far removed from Primitiella as we now believe to be the case. 



Primitiella constricta, n. sp. 



PLATE XLIII,' FIGS. 48-52. 



Size. — (E. C.) Kentucky specimen: Length 0.67 mm.; hight 0.36 mm.; thickness 0.24 mm. 

 Minnesota " '■ 0.60 " " 0.35 " " 0.21 " 



« •' " 0.68 " " 0.33 " " 0.22 " 



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, 



