424 The Avierican NnMiralist. [May, 
Sow. the majority of European forms now known under 
Bayle's Macrochilina. 
In America, Soleniscus is one of the most characteristic 
genera of the Upper Carboniferous. The forms fall naturally 
into two categories: (rt) the elongate or fusiform shells; and 
{b) the subovoid or subglobose varieties. 
Those of the first group predominated in the earlier part of 
the epoch, while those of the second were more abundant in 
the latter part. The fusiform species occur most plentifully in 
the bituminous shales immediately associated with the coal 
seams. This would indicate that these gastropods were marsh 
or brackish-water forms, rather than denizens of the open sea. 
The subovoid forms are more commonly found in calcareous 
strata and were probably more strictly marine than the other 
members of the genus. Aside from the apparent difference in 
optivmm habitat the shells of the two sections present some 
distinctive structural features which, taking all things into 
consideration, may eventually warrant a generic separation. 
This might with advantage be done with the American species, 
but whether it could be satisfactorily applied to the numerous 
foreign forms has not, as yet, been determined. The shells of 
the first category, compared with those of the second, have 
the volutions much more convex, the spire greatly depressed, 
the body whorl relatively much larger, and the aperture corres- 
pondingly ample, while the columellar ridge is usually obtuse 
and sometimes scarcely defined. 
EXPLANATION OF PLATE XX. 
Figs. I, 2. 3. Soleniscus at 
uitus Sow. 4. 5. humilis Keyes. 
5. 5. nnvbcnji ? Stevens. 
6. 5. gracilis Cox. 7. 5. at- 
'ennatits Hall. 8. 5. typic 
■Hs M. & W. 9. 5. attenuatus ? 
Hall. 10. M.primogcmnm 
Conrad. 11. S. klippartiyicQV- 
12, 14. 5. brcvis White. 
13. M. intercalare M. & W. 
[5. M. pouderosum Swallov 
V. 16. 5. paludinceformis Hall. 
17. M. texanum ? ^\vxxm2.xA. 
18. S. planus White. Last five 
ifter White. 
