TltTKANol \ \\IM-ONSINKN8IR WllUliclil. 



MJB. : 



vwnmn>i'n.>i'> Win 1 1 IKI.H. :-> Ann. Rept Oeol. Surv. WIs., p. 76; alao 1882, Oeol. Sunr. 

 WU., TO). Iv, p. 223, pi. vi, fig*. 15, 16. 



ato.-t lii^lit (if >hfll varying in the material l>efore us from s mm. to 37 mm.; 

 closely coiled for the genus, subglobular in form when young, but becoming strongly 

 i. with the last volution less inrolled and the lips greatly expanded laterally 



| 



:i:it al-o above (yet not materially thickened) in the adult form; in the 

 latter the outer lip is deeply notched in the middle, the notch spreading anteriorly 

 more slowly than u-u.il. the lobes on each side rounded-triangular in outline. 

 Dorsal periphery of casts with a broad, revolving band, the top of which may be 

 slightly convex, Hat or concave, the whole increasing in elevation with age; on each 

 side of the central band the inner volutions (as seen in fractured specimens) have 

 tir-t a concave space and then a ridge, but these pertain chiefly to the exterior side 

 of the shell, being only in rare cases, and always with difficulty, distinguishable on 

 casts: inner volutions elongate-reniform in section, outer volution more triangular; 

 umbilicus comparatively small, the width only about one-fifth of the greatest 

 <li.imeter of the shell. Surface markings not fully determined, apparently as in T. 

 obsoleta and T. bidorsata. 



The essential generic characters (i. e., the revolving ridges) were overlooked by 

 1'rof. \V bitfield. Still he noticed the resemblance to the adult form of T. bidorsata, 

 which species he regarded as a Bucania, while his wisconsinenxis he held to be "a 

 true Hellrrophon, as is readily seen by the closed or nearly closed umbilicus." Hut 

 -litlerences in the size of the umbilicus, when other characters agree, are now con- 

 sidered as of small importance. In this case certainly it is not of material 

 consequence. Besides, the umbilicus is not by any means closed, there having 

 been no axial thickening which mi^ht have filled the not very small cavity seen in 

 casts. 



Voting specimens showing the inner volutions of T. u isconsinensia closely resemble 

 those of T. obsoleta, the only difference observable in casts being that the umbilicus 

 is slightly smaller and the volutions more ventricose in the present form. Adult 

 specimens of the two species cannot be confounded, the last volution being higher, 

 with flattened slopes, and less inrolM in '/'. "/><;> ;/n<ww, the whole producing a 

 very differently shaped aperture. T. bid" id T. sfj-mrinnta have more com- 



pressed whorls, much larger umbilicus, ami a wilier as well as otherwise differently 

 shaped mouth, while for both the lateral ridges are conspicuou- features of casts, 

 which is not at all the case in T. vticonsinensis. 



