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 not 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. millert 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 (8) the possession of a rounded, antero-ventrally situated 
tubercle, which is wanting in the Ohio species. 
Formation and locality—Upper third of the Trenton shales, St. Paul and near Cannon Falls, 
Minnesota. 
PRIMITIA MICULA, 2. Sp. 
PLATE XLIII, FIGS. 69—72. 
Sizz.—Lenegth 0.39 mm.; hight 0.25 mm.; thickness 0.23 mm. 
This species, though much. smaller, seems to be related to P. sancti 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. twmidula 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 cylindrica. 
PRIMITIA CELATA, 2. Sp. 
PLATE XLIII, FIGS. 67 and 68, 
Size.—Length 0.57 nm.; 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 
