MUSSEL FAUNA OF THE KANKAKEE BASIN. 



45 



occur at all in the Kankakee Basin, but is common in the Tippecanoe 

 River. We found a few in Tippecanoe Lake. 



12. JJnio gihhosus {Barnes). Lady-finger^ spike, — Unio gihhosus 

 is a common, widely distributed shell, found in all sorts of situations; 

 being one of the common shells of lakes, as well as rivers. 

 The nacre is usually a rather dull purple, which unfits it for the 

 button industry. A white-nacred form is not altogether uncommon. 

 It has a soft satiny luster and can be used commercially. The shells 

 vary in form as well as in color, some being short and humped, more 

 or less closely resembling P. phaseolus^ and others long and sharp, 

 and at times difficult to separate from L. rectus, 



V. gihhosus was one of the most widely distributed shells within 

 the Kankakee Basin, being found at nearly all the stations in the 

 Yellow and Kankakee as well as in the Iroquois and in Fish Lake. 

 It was also found in Tippecanoe Lake. It formed most of the culls 

 in the pearler's pile at Momence. 



Marginal cysts caused by distomids, dorsal baroques, and small 

 round pearls are common in this species. 



One white-nacred shell was found at Plymouth, but as a rule all 

 the shells of the upper parts of the river were deep purple. At 

 Momence these shells exhibited peculiar and interesting phenomena. 

 They seemed to be passing here from the purple-nacred form to the 

 white, and one had all intermediate stages; many were of a beautiful 

 rosy hue throughout, others shaded from blue about the margin 

 through rosy to pale rose. Investigations on other streams have 

 shown similar peculiarities of the color distribution in this shell. 



It is worthy of note that both U. gihhosus and L. rectus become 

 more nearly, or a greater per cent, white-nacred as we go down the 

 Kankakee system, and a careful study here may throw light on the 

 cause of the color in these shells. It may be that the softer waters 

 and amount of humic acid in the upper waters may favor the pur- 

 plish deposit, while the colorless forms which occur shortly after the 

 limestone river bed is reached may be favored by an excess or 

 abundance of lime. 



13. Alasmidonta truncata{B.H. Wright). Elk-toe.— Alasmidonta 

 truncata is a handsome, beautifully rayed shell, attractive to the col- 

 lector, but too thin to be of any service in the manufacture of but- 

 tons. It is not common in the Kankakee Basin. There was a fair 

 number of shells in the clammer's shell pile at Momence and a few 

 j were collected at the mouth of the Iroquois River. 

 I llf. Alasmidonta calceola (Zea).— This shell is too small to have 

 any commercial value. It is a shell of small streams, and is occa- 

 sionally found in lakes. It was quite common in the Yellow River 

 at Plymouth and some examples there reached a very large size for 

 jtbe species. It was found at Forked Creek, near Wilmington, and 

 was there noted as becoming gravid (Aug. 27). 



