362 THE CHICAGO ACADEMY OF SCIENCES. 
horn or light green, showing former peristome marks as in 
decisum, surface polished, smooth save for the somewhat ele- 
vated, crowded growth-lines which roughen the shell to some 
extent; the shell beneath the epidermis is chalky white; apex 
small, similar to decisum, but more prominent; spire elevated, 
elongated, conic; suturesimpressed, almost channeled; whorls 
six to seven in fully adult specimens, rather flat-sided, sloping 
near the sutures, where they are almost angular; the whorl oc- 
cupies three-fourths of the entire length of the shell, and the 
periphery is perceptibly flattened; aperture broadly ovate, 
rounded below and contracted above; forming a sort of “bay” 
at the columella, white or bluish-white within; peristome thin, 
acute, simple, the terminations connected by a rather heavy 
columellar callus which is reflected over the umbilicus; the 
parietal callus is bluish-white and is sometimes bordered by a 
black stripe; base rounded, imperforate, somewhat wrinkled. 
Operculum similar to that of decisum. 
Length, 32.00; width, 20.00; aper. esieet, 17.00; width, 11.00 mill. (10113.) 
rf S10s) 5 1808 “: 16.5055 74" 11.00 “ (10113.) 
os 29.00; se VtDO; ce moeay 8 | Raa 10.00 “ (8857.) 
“ 30.00; “ 18.00; e poe ees UP 7 | ae 10.00 “ (8844.) 
“5 40.00; “ 25.00; ©. LUOe ete. hE ee (9343.) 
Animal; Similar to decisum. 
Radula: Same as that of decisum. 
Distribution: Massachusetts to Illinois and Michigan, 
south to Central Ohio. 
Geological distribution: Pleistocene; Loess. 
Habitat: Similar to decisum. 
Remarks: This species is almost always confounded with 
decisum. It is a more heavy shell, the spire is more produced, 
the aperture is more sigmoid and the whorls are more flat- 
sided. The two species are almost always found associated 
together and it is a question whether they do not interbreed. 
It is certainly very difficult to separate some of the forms of 
these two species. This is the most common Campeloma in 
this region and grows to a large size. In Wolf Lake it is very 
plentiful, and in the North Branch of the Chicago River it is 
quite common and very typical. It is universally distributed 
and has been found fossil on the old lake beaches and by Mr. 
Jensen in sand banks on the lake shore north of Graceland 
avenue, 
