248 



by the characters of the cardinal teeth and the rounded, nonangulate character 

 of the posterior slope. In Unio rubiginoxux there is a well marked ridge extend- 

 ing quite to the posterior margin. The flat and white nacred form also may 

 occasionally be seen in collections as Unio yuuldiawts Lea, now a well recognized 

 synonym. 



Unio fabalis Lea. Twelve specimens from Tippecanoe Lake. 



This is one of the smallest of our Union. The shells submitted do not pre- 

 sent any variant features other than the very light coloration so characteristic of 

 all the lake shells which we have seen. Unio lapillm Say is a synonym. 



Unio gibbosity Barnes. This form is represented by three specimens from 

 Turkey Creek. These are all much thinner and lighter than the same species 

 from the Ohio and Wabash rivers, in both of which it is a common shell. It 

 seems to be very abundant in certain of the lakes of northern Indiana, notably 

 Lake Maxinkuckee. The nacre of these three individuals is very dark purple. 

 Similar shells to these probably have led to the reference of Unio complauatus 

 Solander to the western fauna. 



Unio iris Lea. Two characteristic specimens from Turkey Creek. Like its 

 near relative — which is probably also a sj nonym — Unio iioi'ieboraci Lea, this shell 

 occurs most commonly and abundantly in creeks and other small streams. It 

 most affects soft muddy bottoms in rather still waters. 



Unio luteohiK Lamarck. Ten specimens from Syracuse Lake; seven specimens 

 from Turkey Creek. 



This species is the most widely distributed shell of the family. It occurs 

 in every stream, lake and pond in Indiana in which shell life of any sort occurs 

 at all. It is also the most abundant Unio, and, correlated with abundance and 

 wide distribution, is a range of variations that are of the greatest import in evo- 

 lutionary processes. All the shells submitted, particularly those from Syracuse 

 Lake, are well covered, posteriorly, with carbonate of lime in heavy masses. 

 The lake specimens also have beautifully marked green rays widely separated 

 over a polished disk, thus constituting them the form to which Anthony gave the 

 name of Unio distans. The epidermis usually has the peculiar coloration of 

 forms which live in muddy bottoms, though in the lake specimens the epidermis 

 is, for some hidden chemical reason, quite red posteriorly. This peculiar color- 

 ation has often been noticed in shells submitted to us from the lake region of 

 Northern Indiana. 



Unio Occident Lea. Nine characteristic specimens from Turkey Creek. None 

 present features different from shells found elsewhere in the State. 



Unio pressits Lea. One specimen from Turkey Creek. 



