1048 THE PALEONTOLOGY OF MINNESOTA. 



LTrochonema beachl. 



obscure on all save the last whorl, and here even they are never coarse, though often somewhat irregular. 

 The lines are not quite vertical on the outer or peripheral face crossing it from above somewhat obliquely 

 backward. On the lower side they sweep very strongly backward and grow stronger as they curve over 

 the median angularity into the umbilicus. In the latter the surface is first flat, then convex. Specimens 

 are usually not as large as the one shown in our flg. 2. 



Many of the Stones River group specimens cannot be distinguished from the Trenton form, but 

 occasionally we meet, in Tennessee especially, with a larger variety (see pi. LXXVII, figs. 7 and 8) which 

 may be distinguished as var. latum. Its whorls are less concave on the upper slope and enlarge more 

 rapidly H,han in the ordinary variety. 



In Canada, at Pauquettes rapids, a variety occurs abundantly in the Black River limestone differing 

 from the others in being relatively a little higher, very thin, with the lines of growth finer and more reg- 

 ular, and the umbilical carina sharper. Figures 46 are of a good, though rather young example of this 

 variety. The same form was figured by Salter. It may be called var canadensis. 



Formation and locality. This species is found in the three beds of the Trenton group at many local- 

 ities in Gaodhue and Fillmore counties. We have not noticed it among the numerous Trochonemas of 

 the Stones River group at Minneapolis and other points in the state, but it occurs in this formation in 

 Wisconsin and Illinois ; also in Kentucky, Tennessee. New York and Canada. While it is rather a com- 

 mon fossil through the greater part of the Trenton, and perhaps the Cincinnati period also, good speci- 

 mens, of either casts or shells, must be counted as very rare. There is some doubt about the casts found 

 at Cincinnati. They may or may not belong to this species. 



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

 Museum Register, Nos. 7 HOI, 8727. 



TEOCHONEMA BEACHI ? Whitfield. 



PLATE LXXVII, FIGS. 6-12. 



f Trochonema beachi WHITFIELD, 1878, Ann. Rep. Geol. Sur. Wis., p. 74; also 1882, Geol. Wis., vol. 

 Iv, p. 213. 



We have not been able to satisfy ourselves concerning the species Intended by Prof. Whitfleld to 

 bear this name. It must be very closely related to T. umbilicatum, the only differences to be made out 

 from the single view (dorsal) given by him being a thicker shell (producing the abrupt apertural expansion 

 in the cast) and a slightly greater proportional night of the volutions. The umbilicus is said to be much 

 narrower and more abrupt, the spire higher and the shell smaller. On plate LXXVII, figure 11 repre- 

 sents a section of a small specimen from Dixon, Illinois, having apparently all the characters ascribed to 

 T. beachi. The umbilicus, perhaps, is a trifle too large and the shell matter enclosing it somewhat thinner 

 than in several other specimens that we refer here. The bight of the spire and general appearance of the 

 shell is decidedly like the Canadian Black River variety of T. umbilicatum (see plate LXXVII, figures 46), 

 but the lips are much thinner in that form. Except when the specimens are unusually good, it must 

 always be a difficult matter to recognize T. beachi. 



Formation and locality. Stones River group, Minneapolis, Minnesota; Janesvillc and Beloit, Wis- 

 consin, and Dixon, Illinois. A single example, apparently of the same form, from the Black River group 

 at Curdsville, Kentucky. 



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

 TROCHONEMA BELOITENSE Whitfield. 



PLATE LXXVIII, FIGS. 1-0. 



Trochonema beloitense WHITFIELD, 1878, Ann. Rep. Geol. Sur. Wis., p. 74; and 1882, Geol. Wis., vol. 

 Iv, p. 212. 



Though closely related to T. umbilicatum, this fine species is easily distinguished by its much more 

 rapidly expanding and higher volutions, giving to the last whorl a much more ventrlcose appearance. 



