54 Lake Maxinkuckee, Physical and Biological Survey 



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 clam- 

 mers. The old shells develop into a peculiar form, being flattened, 

 arcuate along the ventral border and very thin posteriorly, so that 

 they usually crack badly in drying; they represent the form de- 

 scribed by Simpson as var. delicata. In general outline they re- 

 mind one somewhat of Margaritana 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 gibbosus is very constant in its char- 

 acters, 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 purple, never varying to pink 

 or white as it frequently does in rivers. 



Like Lampsilis luteola this species is frequently preyed upon by 

 muskrats and the cleaned out shells are common where these ro- 

 dents have had their feasts. 



Although U. gibbosus of the Tippecanoe River near the mouth 

 of the Outlet is very commonly infested with a distomid parasite 

 along the 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 ing ens. 



Even the large strong river shells of Unio gibbosus have no 

 value in the manufacture of buttoms because of their purple color 

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



The only other lake examples with which the Lake Maxinkuckee 

 specimens of this species have been compared, are some collected in 

 Lake Erie at Put-in-Bay. The Lake Erie shells are much unlike 

 the Maxinkuckee specimens, being short, humped and remarkably 

 solid and heavy. Similar shells to those of Lake Erie are found in 

 some of the small southern rivers. 



We have no notes referring to gravid examples in the lake. 

 This was probably because the most active work in collecting and 

 examining mussels was carried on in the autumn, and the breeding 

 period of this species is in early summer. 



