§30 THE PALEONTOLOGY OF MINNESOTA. 
[Archinacella depressa. 
half the hight of the shell, projecting distinctly beyond the margin. Surface with 
well marked sublamellose lines of growth, averaging in the outer half about 1 mm. 
apart. Length 32 mm.; width 26 mm.; greatest hight 11 mm.; hight of apex 5 mm. 
This species resembles A. powersi, but may be distinguished at once by the 
contour of its aperture, the margins being strongly arched in that species while in 
this one they are horizontal. The surface markings are also stronger in A. cingulata, 
while the anterior outline is broader, the apex projects farther forward and the 
transverse section of the shell is more convex, especially in the post-central region. 
A, patelliformis Hall sp., and A. simulatriz, though much smaller, are probably more 
intimately related to A. cingulata than is A. powerst. 
Formation and localily.—Trenton group, Amygdalocystites bed, Mercer county, Kentucky. 
Collection.—E. O. Ulrich. 
ARCHINACELLA DEPRESSA, ”. Sp. 
PLATE LXI, FIGS. 8 and 9. 
Shell of medium size, depressed-conical, the outline almost regularly oval, 
rather wide; the width and length about as seven is to eight; apex situated about 
one-seventh of the length from the anterior margin; the point, which is a little 
imperfect in the specimen, seems not to have been much elevated or incurved; 
apertural margin arched. Surface exhibiting a few obscure concentric lines. 
Muscular scars not observed. Length 20.5 mm.; width 18 mm.; greatest hight (at 
apex) about 5.2 mm. 
This shell agrees with A. powersi in the arched apertural margin and broad 
form, but differs decidedly in having the apex situated some distance from the 
margin. As the convexity of the shell also is somewhat less, the profiles are 
different. There is also a slight difference in the outline as seen from above. In all 
these features the species approaches A. perovalis Whitfield sp., but it is readily 
distinguished from that species by its greater width and lower form. 
Formation and locality.—Stone’s River group, Vanuxemia bed, Minneapolis. 
Collection.—Geological and Natural History Survey of Minnesota. 
Museum Register, No. 5523. 
ARCHINACELLA PEROVALIS Whitfield sp. 
PLATE LXXXII, FIGS. 3 and 4, 
Metoptoma perovalis WHITFIELD, 1878, Ann. Rept. Geol. Surv. Wis., p. 74; 1882, Geol. Wis., vol. iv, p. 
211, pl. v, figs. 13 and 14. 
Metoptoma explanata SARDESON, 1892, Bull. Minn. Acad. Nat. Sci., vol. iii, p. 336. 
This species agrees very closely with A. depressa, the only difference of any 
consequence that we can now point out being the greater width of that shell. In 
