s:u 



.1 i*r.n<ili< tin- width i- to the length about as eleven is to fifteen, while in the 

 other it i- :. is to eight. Sp.-ciin.Mis vary in length from 16 to 80 mm. The 



imiM-ular scan, so far as they have been determined, agree very well with those of 

 .1. /.//>/-,/. The apertural margin is slightly arched, and the surface appears to 

 havo been nearly smooth. 



U Inui.'M 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 

 Whim. !!'- ti-mv-. It seems, therefore, to us that the slight anterior truncation 

 exhibited by the type specimen may be due to some abnormal cause. 



Fnrmabo* and locality. Stone's Rivor group, Vanuxemla bed, Minneapolis, Minnesota, and Beloit, 

 Wisconsin. 



ARCHINACBLLA DBLKTA Sardeson sp. 



1-I.ATE I.XI. FI08. !-. 



Cnri*<trop* delete BARDKAON, 1892, Bull. Minn. Acad. Mat. Scl., vol. Ill, 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 

 I'fhind 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.; bight 

 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 inner sides of dead shells of Protoicnrlhin pervoluta and Holopea obliqua, 

 are now represented by a biconvex fossil reminding one greatly of casts of some 

 disciimid hrachiopod. Two of these specimens are represented on plate LXI. 



This is the lir-t of a ^roup of species that seems to be related to^A. (Carinarop- 

 sis) fakUii:rmis Hall (Pal. N. T., vol. i. p. 1S3; 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 Hiver 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 iit?llif<>rmis, ah of them having a nearly smooth surface, 

 while Mall's species according to his figures and descriptions has the surface marK--<! 



