50 MUSSEL FAUNA OF THE KANKAKEE BASIN. 



this species are used in the button-making industry than any other 

 single species. It is not so good a shell as the niggerhead and a few 

 others, but is one of the commonest and most widely distributed and 

 the material is very good. 



This species is not found in lakes and is not common in the smaller 

 streams. It occurs throughout the length of the Yellow and Kan- 

 kakee Rivers, but is rather scattered in the Yellow and upper Kan- 

 kakee. In the lower Kankakee it is found at every station, and began 

 markedly increasing in numbers about Sheldon, Ind. It formed the 

 main mass of shells in the pearler's pile at Momence, 111., and fine 

 examples were seen in a pile of shells left by a pearler below 

 Momence. It was also found in considerable numbers at Custer Park, 

 Wilmington, and at the mouth of the Kankakee. In the Iroquois 

 River it was found at L'Erable and near the mouth. A large num- 

 ber were gravid at Momence, August 23. 



32. Lampsilis luteolus {Lamarck) . Fat mucket. — Lamjjsilis luteoliis 

 is a quite variable shell. It is inferior to the mucket on account of 

 being smaller and more cylindrical, and the greater curvature of the 

 valves makes it harder to work up satisfactorily. Such large fine 

 specimens as occur in some rivers, e. g., the St. Joseph River at Fort 

 Wayne, Ind., would make excellent buttons, but these are not 

 common. 



It is one of the most abundant and widely distributed shells and is 

 usually found in lakes and in small rivers. In the Kankakee Basin 

 it occurred at almost every station, in lakes, rivers, and streams alike. 



In parts of the Kankakee Basin this species is of especial interest, 

 as many of the examples found are infested with a parasite which 

 leads to the formation of perfect spherical pearls. The pearls are all 

 of small size and on this account not of enough value to justify work- 

 ing them. They are, however, of great scientific interest, as they 

 offer unusual opportunities for the study of pearl formation. In 

 places a single mussel Avill contain as many as a half dozen or more 

 pearls, and the average will run more than a pearl per mussel. A lot 

 of material was collected which furnished fine sections showing the 

 epithelial sac in Avhich pearls are formed. It also indicated the 

 cause of pearl formation to be probably a small distomid which 

 formed cysts in the mantle of the mussels. It was greatly hoped that 

 opportunities would be given to follow up this subject further, but 

 this hope has not been realized. This field offers excellent oppor- 

 tunities to the investigator. 



33. Lampsilis midtiradiatus {Lea). — This very pretty, much-rayed 

 shell resembles Lam/psilis ventricosus in general form, but is too small 

 and thin to be of any service in the manufacture of buttons. It was 

 not found in the Kankakee Basin at all, but was not rare in Tippe- 

 canoe Lake and River. 



