THE NATURAL HISTORY SURVEY. 361 
buried from sight. Sometimes, when found ina quiet nook, 
they may be seen crawling over the surface of the mud. They 
seem to prefer large bodies of water. 
Remarks: This species is rare in this region, and the 
specimens found are not typical. Professor Call remarked that 
of a lot of Campeloma sent him only 5 per cent were decisum, 
the others being sabsolidum. Many specimens are similar to 
vufum, but the pink shell will always distinguish that species. 
It is always confounded with subsolidum, and many of its va- 
rieties are difficult to distinguish from that species. Decisum 
has well-rounded whorls, a somewhat depressed spire, broadly 
conical, and the epidermis is of a beautiful green. Swbsolidum 
has always a more solid shell, with a longer spire, more flat- 
sided whorls and (in this region) a greenish horn-colored shell. 
In a lot of specimens from Wolf Lake, the females (July 
16, 1896) were filled with ova in an advanced stage of devel- 
Opment. One specimen had twenty ova measuring 5 mill. in 
diameter, and the yolk was of a beautiful transparent horn 
color. 
The oviduct of this species is infested by a parasite, Heter- 
ostromum echinatum Diesing, which is found in considerable 
numbers, and the intestine is tenanted by another parasite, Ano- 
plophrya vermicularis. 
On February 23, 1897, a specimen of this species gave 
birth to six young which were very active. A few days later 
she added twelve more to that number, making eighteen in all. 
The young all died three weeks after birth. When born the 
animal is very transparent and vitreous, with a very large foot. 
The shell is 3 mill. in length, and consists of about two whorls. 
The operculum is very thin and transparent, almost structure- 
less, and measures 1% by 1 mill. The shell might easily be 
mistaken for Ammnicola imosa. No reversed specimens occurred 
in this brood. (Mus. No. 12353.) 
Decisum is found, rather sparingly, however, in all parts of 
the territory. On the old lake beaches it may be found ina 
fossil condition. 
150. Campeloma subsolidum Anthony, pl). xxxvi, figs. 8-12. 
Paludina subsolida ANTHONY, Proc. Phil. Acad., p. 71, 1860. 
Paludina exilis ANTHONY, 1. ¢c., p. 71, 1860. 
Paludina milesit LEA, |. c., p. 156, 1863. 
Shell: Elongate, very solid, more or less malleated; color 
