OSTRACODA. 653 



Primitia micula.] 



slightly oblique, deepest in its lower part, narrowing above by the development of a 

 low swelling on each side, that on the anterior side more prominent than the other; 

 a nob very prominent, rounded tubercle near the lower part of the anterior border; 

 excepting the sulcus and the flattened border, the entire surface is beautifully 

 reticulated. 



This fine species is probably more closely related to P. milleri Ulrich, from the 

 upper beds of the Cincinnati group, than to any other known. The size of -P. milleri 

 is somewhat greater, its length being usually a little more than 1.0 mm. But the 

 real differences between the two forms are (1) the proportionally greater length of 

 the valves and of the hinge in the Minnesota species; (2) its longer and otherwise 

 different sulcus, and (3) the possession of a rounded, antero-ventrally situated 

 tubercle, which is wanting in the Ohio species. 



Formation and locality.— XJpiieT third of the Trenton shales, St. Paul and near Cannon Falls, 

 Minnesota. 



Primitia micula, n. sp. 



PLATE XLIII, FIGS. 09-72.' 



Size.— Length 0.39 mm.; hight 0.25 mm.; thickness 0.23 mm. 



This species, though much smaller, seems to be related to P. sandi pauli. It is 

 however relatively shorter, with a longer hinge line and stronger dorsal angles. The 

 valve is strongly convex, especially in the posterior half, and the prominences on 

 each side of the curved sulcus are decidedly higher than in the larger species. 

 Again, that species has a rounded tubercle in front which is wanting in P. micula. 

 Finally, the surface is only obscurely punctate and not reticulate. 



It is perhaps more closely related to P. tumidula of the Hudson River shales, 

 but, aside from its much smaller size, it is at once distinguished by the absence of 

 the narrow curved ridge, running a short distance within the ventral margin in that 

 species. 



Formation and locality. — Galena shales near Cannon Falls, Minnesota; associated with P. uphami, 

 Schmidtella affinis and Bythocypris cylindriea. 



Peimitia celata, n. sp. 



PLATE XLIII, PIGS. 67 and 68. 



Size.— Length 0.57 mm.; hight 0.33 mm.; thickness 0.30 mm. 



Valves with the back long, straight or gently arcuate, the dorsal angles distinct 

 though not sharp, the ends about equally curved though the anterior is somewhat 

 narrower than the posterior; ventral and anterior margins together following a 

 semielliptic. curve; free edges grooved, the true contact margins concealed by a 



