834 THE PALEONTOLOGY OF MINNESOTA. 



[Archlnacella Bubrotunda. 



AKCHINACELLA SCBROTUNDA, n. sv. 



PLATE LXI, FIGS. 26 and 27. 



Shell rather small, strongly convex, broadly oval, or nearly circular, obliquely 

 conical, with the apex obtusely pointed, not incurved, and situated close to the 

 anterior edge; aperture slightly arched; beneath the apex, in a side view, the 

 anterior outline is scarcely concave; backward from the apex the outline is gently 

 convex, the highest point being about midway between the apex and the middle of 

 the shell. Surface nearly smooth, exhibiting in the best specimens only three or 

 four, distant, impressed concentric lines. Length 13 mm.; width 11.3 mm.; hight 

 5.5 mm.; hight of apex 4.5 mm. 



This species is associated with A. deleta Sardeson sp., and A. instabilis var. 

 incurva. From the first it is easily distinguished by its rounded (much wider) form, 

 while in the second the apex is drawn out into a small involute projection, giving it 

 a very different outline in the side view. The species is related probably also to 

 A. (Tryblidium) pileolum Whitfield, A. (Metoptoma) simplex Billings, and A. (Metop- 

 toma) estella Billings, but we cannot consider it identical with any of them. 



Formation and locality. Black River group, Ctenodonta bed, Goodhue county, Minnesota. 

 Collection. E. O. Ulrich. 



AKCHINACELLA RICHMONDENSIS, n. sp. (Ulrich.) 



PLATE LXI, FIGS. 6 and 7. 



Comp. Tryblidium indianetux MILLEK, 1891, Adv. Sh. 17th Rep. Geol. Surv. Ind., p. 85. 



Shell above the medium size, subovate in outline, obliquely conical, with the 

 apex obtusely pointed, not incurved, and situated about one-sixth of the length 

 behind the anterior margin; in a side view the anterior slope is slightly concave, 

 while the slope backward from the apex is correspondingly convex, with the highest 

 point near the apex; aperture nearly or quite horizontal. Surface marked by 

 rather distant concentric lines. Length 24 mm.; width 20 mm.; hight 6.5 mm. 



This species reminds one considerably of the geologically older A. depressa, but 

 the arched aperture, lesser convexity and somewhat different outline of that species 

 are sufficient proof of their distinction. It is probably more nearly related to A. 

 subrotunda, but in this case we have obvious differences in outlines and in the 

 position of the apex. We could come to no positive conclusion respecting Miller's 

 Tryblidium indianense, but if his description is reliable it is certainly distinct. 



Formation and locality. Richmond group of the Cincinnati period, Richmond, Indiana. 

 Collection.-^. O. Ulrich. 



