GASTROPODA. 879 
Tetranota macra.] 
and width being respectively as two is to five. The dorsal ridges differ in this that 
the centro-lateral pair continues in full strength almost or quite to the apertural 
margin. There is besides a lateral pair of ridges, not so strong as the others though 
still quite distinct, making in all six revolving ridges. This outermost pair may 
occasionally appear to be represented in 7’. bidorsata, though never so distinctly; 
yet when carefully compared it will be noticed that T. sexcarinata really has an 
extra pair, since the ones which in Hall’s species form the extreme lateral bound- 
aries of the volutions, and at the same time the edge of the umbilicus, are present 
also in T. sexcarinata. The umbilicus is of about the same size and character in the 
two species, but the mouth and surface markings are different. The sinus in the 
outer lip, namely, is deeper and much wider, the backward sweep of the lines of 
growth beginning already between the edge of the umbilicus and the outer ridge 
instead of at the centro-lateral ridge. Furthermore, the lines are much farther 
apart and coarser, the distance from line to line averaging about 1 mm. Finally, 
the lines of growth are, though more or less obscurely, reproduced on casts of the 
interior, while no trace of them is observable on casts of the other species. 
With the differences mentioned there can be no reasonable doubt about the 
specific distinctness of T. sexcarinata and T. bidorsata; and the others are still farther 
removed. Good adult specimens cannot be confused, only the young being 
sufficiently alike to render separation difficult. 
Formation and locality—Stones River group (Vanuxemia bed), Minneapolis, St. Paul and Cannon 
Falls, Minnesota; Beloit and Janesville, Wisconsin; Dixon, I1l.; Lebanon and Lavergne, Tennessee. Tren- 
ton group (Fusispira bed), Fillmore county, Minnesota. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich. 
Museum Register, Nos. 5064, 7530. 
TETRANOTA MACRA, 2. Sp. 
PLATE LXV, FIGS. 1 and 2, 
This species reminds one in its markings of 7. sexcarinata, but has only four 
dorsal ridges. The lines of growth also are stronger, showing distinctly on casts. 
The umbilicus is relatively larger than in any of the other species of the genus and 
the sides of the volutions more sharply angular. Corresponding differences occur 
in the form of the aperture, 
Formation and locality,n—Vanuxemia bed, Stones River group, Minneapolis, Minnesota. 
Collection.—E. O. Ulrich. 
