GASTROPODA. 831 
Archinacella deleta.] 
A. perovalis the width is to the length about as eleven is to fifteen, while in the 
other it is as seven is to eight. Specimens vary in length from 16 to 30mm, The 
muscular scars, so far as they have been determined, agree very well with those of 
A, powersi. The apertural margin is slightly arched, and the surface appears to 
have been nearly smooth. 
Whitfield describes and figures this species as being flattened and truncate in 
front, and the absence of anything of the kind in the Minnesota specimens led Mr. 
Sardeson into giving a new name to the latter. We also failed to notice such a 
feature in any specimen, even those from Beloit, Wisconsin, the typical locality for 
the species, being without it, though agreeing in every other particular with 
Whitfield’s figures. It seems, therefore, to us that the slight anterior truncation 
exhibited by the type specimen may be due to some abnormal cause. 
Formation and locality.—Stone’s River group, Vanuxemia bed, Minneapolis, Minnesota, and Beloit, 
Wisconsin. 
ARCHINACELLA DELETA Sardeson sp. 
PLATE LXI, FIGS. 16—20. 
Carinaropsis deleta SARDESON, 1892, Bull. Minn. Acad. Nat. Sci., vol. ili, p. 335. 
Shell small, obliquely subconical, rather convex, elliptical in outline, the width 
and length usually as three is to four; aperture nearly horizontal; embryonic shell 
very small, involute, forming about one volution, rarely preserved, the apex usually 
appearing as but little incurved; the apex situated constantly a short distance 
behind the anterior margin. Surface almost smooth, occasionally exhibiting a few 
lines of growth. Length 9.25 mm.; width 7.1 mm.; greatest hight 4.25 mm.; hight 
of apex about 3 mm. 
This species commonly grew upon the shells of other mollusks and it is often 
attached to them. We have before us several specimens that, having grown upon 
the concave inuer sides of dead shells of Protowarthia pervoluta and Holopea obliqua, 
are now represented by a biconvex fossil reminding one greatly of casts of some 
discinoid brachiopod. ‘Two of these specimens are represented on plate LXI. 
This is the first of a group of species that seems to be related to A. (Carinarop- 
sis) patelliformis Hall (Pal. N. Y., vol. i, p. 183; 1847). One or the other of these 
forms occurs in, or in the equivalent of, every one of the principal beds between 
the base of the Black River group and the top of the Cincinnati formation. None 
of the western and northwestern species however seem to be strictly identical with 
the New York types of patelliformis, all of them having a nearly smooth surface, 
while Hall’s species according to his figures and descriptions has the surface marked 
