265 



It is found wherever the other mussels are; that is, in sandy or some- 

 what marly bottom in rather shallow water most of the way around 

 the lake, and in the shell-bed in Lost Lake below Bardsley's. In Lake 

 Maxinkuckee one of the best beds is at Long Point. It is abundant also 

 at Norris Inlet, and by McDonald's and Farrar's. 



No very young of this species were found in the lake; they are, 

 however, hard to find in numbers anywhere, even in rivers where the 

 species is abundant — except in cases where portions of the river go 

 almost dry, and this of course never happens to the beds in the lake. 

 The half-grown examples are solid, rather cylindrical shells, the same 

 neat form that is known as the "spike" among the clammers. The 

 old shells develop into a peculiar form, being flattened, arcuate along 

 the ventral border and very thin posterioi'ly, so that they usually crack 

 badly in drying; they represent the form described by Simpson as vai. 

 delicata. In general outline they remind one somewhat of Margaritnna 

 monodonta. This form is not strictly confined to the lake; some similar 

 shells were collected in the Wabash near Terre Haute. 



As found in the lake, Unio gibbosua is very constant in its charac- 

 ters, the only noteworthy difference between individuals being the change 

 in shape already referred to as being due to age. In rivers this shell 

 exhibits considerable variation in shape, size, color of nacre, etc., but the 

 shells of the lake are quite constant in almost every respect. The nacre 

 is a deep pui-ple, never varying to pink or white as it frequently does in 

 rivers. 



Like Lauipsilis luteola this species is frequently preyed upon by 

 muskrats and the cleaned out shells are common where these rodents 

 have had their feasts. 



Although U. gibbosus of the Tippecanoe River near the mouth of the 

 Outlet are very commonly infested with a distomid parasite along tho 

 hinge-line which brings about the formation of irregular baroques, this 

 parasite does not occur in the lake so far as known. Small species of 

 Atax are common parasites of this species in the lake, and in 1909 one 

 was found affected by the large Atax ingens. 



Even the large strong river shells of Unio gibbosus have as yet 

 no value in the manufacture of buttons because of their purple color, 

 and lack of luster. (The white-nacred shells are sometimes used.) 



