862 THE PALEONTOLOGY OF MINNESOTA. 



LOyrtolites retrorsus. 



specimens referred to C. ornatus by Prof. Safford. If any are in doubt, then it is 

 those which he obtained from his "Orthis bed," which, like the Clitambonites bed in 

 Minnesota, we place at the base of the Trenton group. The same form occurs also 

 in equivalent strata in Kentucky, but none of the specimens seen by us are suffici- 

 ently perfect to permit of a positive decision in the matter. So far as the form of 

 the shell and volutions is concerned, the specimens in question certainly agree very 

 closely with C. retrorsus, and, if appearances are not deceptive, they are like it also 

 in the backward swing of the surface markings. The evidence at hand, therefore, 

 seems to indicate that all of the Tennessee and Kentucky Trenton specimens 

 hitherto referred to Cyrtolites ornatus really belong to C. retrorsus. 



.Formation and locality. Upper part of the Trenton group between Burgin and Danville, Kentucky, 

 and Nashville, Tennessee. Probably also In the lower part of the group near the same localities. About 

 ten specimens, mostly casts of the interior, have been found by one of the authors in the upper part of 

 the Trenton group and in the lower part of the Utica group at Cincinnati, Ohio, and at Covington and 

 Newport in Kentucky. 



Collections. E. O. Ulrich; Prof. J. M. SafforY 



CYRTOLITES RETRORSUS, var. FILLMORENSIS, n.var. 



PLATE LXII, FIGS. 38 and 39. 



Under this name we propose arranging provisionally a form occurring not very 

 rarely in the shales of the Black River group at localities in Fillmore county. 

 Unfortunately, none of the specimens before us are in a good state of preservation, 

 all excepting three being more or less distorted casts of the interior. On two of the 

 excepted specimens the shell is preserved on the inner volutions only, while the 

 the third retains a few lines near the aperture. So far as can be determined, the 

 variety differs from the typical form of the species only in having the sides of the 

 inner volutions almost rounded, the form of the outer volution and the surface 

 ornamentation being apparently as in C. retrorsus. The rounded character of the 

 sides of the inner volutions in this, the oldest known variety of the genus, is a 

 noteworthy feature, since it may give us a clue to the origin of the genus. 



.Formation and locality. Black River group, Ctenodonta bed, Chatfleld and near Fountain, Minnesota. 

 Collections. Geological and Natural History Survey of Minnesota; E. O. Ulrich. 

 Museum Register, Nos. 4051, 7535. 



CYRTOLITES OARINATUS Miller. 



PLATE LXII. F1G8. 50-52. 



Cyrtolites carinntus MILI.KH, 1874, Cin. Quar. Jour. Sci., vol. i, p. 311, fig. 32. 

 Coiup. Cyrtolites conradi HALL, 1862, Geol. Rep. Wis., p. 55. (Figured only.) 



Smaller than C. ornatus, the size being about as in C. retrorsus, the average 

 diameter about 13 mm.; in two of our specimens it exceeds 20 mm. Sides sharply 



