830 THE PALEONTOLOGY OF MINNESOTA. 



[Archluacella 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. simulatrix, though much smaller, are probably more 

 intimately related to A. cingulata than is A. powersi. 



Formation and locality. Trenton group, Amygdalocystites bed, Mercer county, Kentucky. 

 Collection. E. O. Ulrich. 



ARCHINAOELLA DEPRESSA, n. sp. 



PLATE LXI, PIGS. 8 and 0. 



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, Vanuxeruia bed, Minneapolis. 

 Collection. Geological and Natural History Survey of Minnesota. 

 Museum Register, No. 5523. 



AKCHINACELLA PEROVALIS Whitfield sp. 



PLATE LXXXII, FIGS. 3 and 4. 



Metoptoma perovalis WHITFIELD, 1878, Ann. Kept. Geol. Surv. Wis., p. 74; 1882, Geol. Wis., vol. iv, p. 



211, pi. v, flgs. 13 and 14. 

 Metoptoma explanata SABDESON, 1892, Bull. Minn. Acad. Nat. Sci., vol. ill, p. 336. 



This species agrees very closely with A. depressa, the only difierence of any 

 consequence that we can now point out being the greater width of that shell. In 



