652 THE PALEONTOLOGY OF MINNESOTA. 
{Primitia mammata. 
Though smaller and proportionally higher behind, this neat Primitia seems to 
be more closely related to P. variolata Jones and Holl, from the Wenloch of England, 
than to any American species. Still there is a regularity about the arrangement of 
the punctz that is wanting in that species. In P. trigonalis, of‘the same authors 
and formation, the ornamentation is similar, but in other respects the species are 
quite different. 
Named for Mr. Warren Upham, of the Geological Survey of Minnesota, whose 
published work has aided materially in advancing our knowledge of American 
geology. 
Formation and locality.—Galena shales near Cannon Falls, Minnesota. 
PRIMITIA MAMMATA, 2. Sp. 
PLATE XLIII, FIGS. 78—81. 
Sizz.—Length 0.51 mm.; hight 0.30 mm ; thickness 0.18 mm. 
Valves suboblong, the marginal portions somewhat depressed, while the central 
parts are slightly swollen beneath and on each side of the sulcus, the latter narrow- 
ing dorsally; back straight, dorsal angles rounded; posterior margin strongly rounded 
in the middle, ventral margin gently convex, subparallel with the hinge line; ante- 
rior outline most prominent in the upper part, the whole sweeping slightly backward; 
edges simple, surface without ornament. 
The slight prominence of the surface about the sulcus gives.this carapace an 
appearance that is not shared by any of the more simple forms of the genus. We 
are somewhat reminded of P. twmidula and P. duplicata,—indeed, | at first confounded 
it with the latter. The first is much more convex, shorter and larger, while perfect 
valves of the second will be distinguished at once by their double borders. P. cen- 
tralis Ulrich, of the Utica horizon of the Cincinnati group, is similar in shape, but 
has a simply convex surface and the sulcus confined to a subcentral pit. 
Formation and locality.—Lower third of the Trenton shales, Minneapolis, Minnesota, 
PRIMITIA SANCTI PAULI, 2%. Sp. 
PLATE XLIII, FIGS. 738 and 74. 
Size.—Length 0.86 mm.; hight 0.56 mm.; thickness 0.38 mm. 
Valves strongly convex, thickest posteriorly, subovate in outline, with a straight 
back nearly three-fourths as long as the greatest length of the carapace, and rather 
distinct dorsal angles; ends rounded, subequal, the anterior sometimes a trifle narrower 
than the posterior; ventral margin broadly convex, free edges with a well-defined, . 
narrow border; sulcus well developed, situated a little in front of the midlength, 
