866 THE PALEONTOLOGY OF MINNESOTA. 



[Oyrtolltina. 



the type of a new genus intermediate in position between Carinaropsis and 

 Cyrtohtes. 



Formation and locality. Ctenodonta bed of the Black River group, Goodhue county, Minnesota 

 The Wisconsin specimen seems to be from an equivalent horizon at Beloit. 



Collections. University of Wisconsin; E. O. Ulrich. 



Genus CYRTOLITINA, n. gen. 



Cyrtolites (part.), ULRICD, 1879, Jour. Gin. Soc. Nat. Hist., vol. ii, p. 12. LINDSTHO'M, 1884, Silurian 

 Gastropoda of Gotland, pp. 82-84. 



For generic characters see page 847. 



The five species at present believed to have the characters of this genus were 

 originally all referred to Cyrtolites. They are, however, quite distinct from the 

 typical species (ornatus) of that genus, and, in certain respects at least, nearer to 

 Bucania and Conradella. With the latter genera they agree in the surface sculpture, 

 in having the aperture distinctly emarginated, and in possessing a slit-band, while 

 they differ in these features from Cyrtolites. On the other hand the agreement with 

 Cyrlolites is stronger only in the form of the volutions and in their number, the 

 whorls being much less in number and higher than wide instead of the reverse as in 

 Bucania. It is difficult to decide as to the relative merits 6*f these agreements, and, 

 as we are scarcely beyond the threshold of knowledge respecting the Paleozoic 

 Gastropoda, we will not presume to attempt it. Still, while we pay tribute to 

 prevailing opinions in both the selection of the new name and in referring the genus 

 to the Cyrtolitidce, it is to be understood that the arrangement is less in accordance 

 with our views than if we had placed it among the Bucaniida>. To this statement 

 we may add the suggestion that Cyrtolitina may have been derived from some form 

 of Bucania like B. subangulata. 



Comparing Cyrtolitina with its possible relatives we find that it diifers from 

 Cyrtolites in having a slit-band, less carinate dorsum, an apertural emargination, 

 higher (more compressed) volutions, and surface markings that are to be called lamel- 

 lose rather than reticulated; from Bucania in having fewer and laterally instead of 

 vertically compressed volutions; and from Conradella in having fewer and more 

 rapidly enlarging volutions, much shorter apertural slit, no distinct dorsal keel, and 

 the subimbricating surface lamellae curved strongly backward on the dorsum. 



CYRTOLITINA NITIDULA Ulrich. 



PLATE LXII, FIGS. 53-55. 



Cyrtolites nitidulus ULKICII, 1879, Jour. Cin. Soc. Nat. Hist., vol. ii, p. 12. 



Shell small, 6 to 8 mm. in diameter; volutions about two, rapidly increasing in 

 size, the outer embracing quite a half of the inner; dorsum blunt, thick, flattened 



