THE NATURAL HISTORY SURVEY. 361 



buried from sight. Sometimes, when found in a 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 subsolidum. Many specimens are similar to 

 rufum, 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. Subsolidum 

 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 15^ by I mill. The shell might easily be 

 mistaken for Amnicola limosa. 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 in a 

 fossil condition. 



150. Campeloma subsolidum Anthony, pi. xxxvi, figs. 8-12. 

 Paludina subsolida ANTHONY, Proc. Phil. Acad., p. 71, 1860. 

 Pahidina exilis ANTHONY, 1. c., p. 71, 1860. 

 Paludina milesii LEA, 1. c., p. 156, 1863. 



Shell: Elongate, very solid, more or less malleated; color 



