642 THE PALEONTOLOGY OF MINNESOTA. 



LSchmldtella incompta. 

 SCHMIDTELLA INCOMPTA, tl. Sp. 

 PLATE XLIII. FIGS. 30-41. PLATE XLV, FIGS. 27, 32 and 33. 



S\7.K. (R. V.) Length 1.1 mm.; bight 0.8 mm.; thickness 0.28 mm. 



" " 0.9 " " 0.85 " " 0.18 " var. sutow/wah's. 



Valves moderately convex, dorsal margin straight, about half as long as the 

 valve; ends nearly or quite equal, ventral outline regularly curved; surface highest 

 a little above and behind the center, the dorsal slope convex but not projecting 

 beyond the hinge line, the ventral slope long, gentle and straight or faintly concave, 

 the wide border being almost obsolete. 



Of this species we have two varieties, one occurring in the lower part of the 

 Trenton shales, the other in the upper part of the Galena shales. The earlier or 

 typical form (plate XLV, figs. 27, 32 and 33), is a trifle more convex and blunter at 

 the dorsal edge, slightly shorter and less equilateral than the other. That the 

 Galena variety constantly developed these minute peculiarities is shown by about 

 fifty valves. Should a subordinate name be desirable, it might be called var. 

 subatqualis. 



The dorsum is less tumid in this species than in any of the preceding. On the 

 whole it may be considered as marking an approach toward Aparchites. Still, the 

 prominence of the surface in the post-dorsal third, though not strong, indicates a 

 relation to S. affinis. A species occurs in the Birdseye at High Bridge, Kentucky, 

 that seems to be intermediate between this species and S. umbonata. 



Formation and locality. Typical form, lower part of the Trenton shales, Fountain, Minnesota; 

 var. mtini-<i>tnlis, upper part of the Galena shales near Cannon Falls, Minnesota. 



SCHMIDTELLA BREVIS, n. sp. 



PLATE XLV, FIGS. 34 and X>. 



SIZE. (L. V.) Length 0.8 mm.; hight 0.65 mm.; thickness 0.2 mm. 



Valves short, subovate, the oval being formed by drawing out the anterior end; 

 dorsum short, gently arcuate, and projecting slightly above the straight hinge line; 

 border inconspicuous. 



In most respects this species is much like its associate, S. incompta, but the valves 

 are much shorter, the dorsal outline is not straight, and the anterior margin is more 

 narrowly rounded. Polycope sublenticularis Jones, from the Anticosti group, has a 

 similar outline, but seems to be uniformly convex which is not the case with the 

 species under consideration. 



forma/ion ami locality. Rare in the Inw.-r part, of the Trunton shales near Fountain, Minnesota. 



