834 THE PALEONTOLOGY OF MINNESOTA. 
[Archinacella subrotunda. 
ARCHINACELLA SUBROTUNDA, 2. SD. 
PLATE LXI, FISS. 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. 
ARCHINACELLA RICHMONDENSIS, n. sp. (Ulrich.) 
PLATE LXI, FIGS. 6 and 7. 
Comp. Tryblidium indianense MILLER, 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.—K. O. Ulrich. 
