652 T1IK PALEONTOLOGY OF MINNESOTA. 



[PriiiiHia m:imm:itit. 



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 punctie 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 Upbam, 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. 



PHIMITIA MAMMATA, n. sp. 



PLATE XMII. FIGS. 78-81. 



SIZE. Length 0.51 mm.; night 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. tumidulu and P. duplicate, indeed, I 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. 



PHIMITIA SANCTI PAULI, n. sp. 



I'1,ATK XMII. FK;s. ::; :m<l 74. 

 M/K. L.'iinth O.Mi nun.: highl o.fjii 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 midleugth, 



