151] FAUNA OF BIG VERMILION RIVER— BAKER 53 



of abnormalities consist of cyst-like pearly growths near the posterior 

 end, in or near the adductor muscle and pallial line. These may occur 

 in one or both valves. Occasionally the anterior adductor scar is almost 

 wholly changed in character by these abnormal growths. In several shells 

 the space between the pallial line and the margin of the valve is stained 

 purple or brown, accompanied by few or many blisters of various sized. 

 The posterior end of the shell may also be affected so that it ceases to grow, 

 forming a blunt posterior end marked by blisters and discolorations. 

 Whether this condition is due to distomid infection as mentioned by 

 Wilson and Clark (1912 63) as occurring in Actinonaias ligamentina from 

 the Maum^ee River is not known definitely, but the inference is strong that 

 it is. It is noteworthy that the largest number of individuals affected by 

 parasitism or other injurious agencies occurred in the upper part of the 

 Salt Fork above Homer Park dam. Specimens collected from stations 

 below the dam, including Middle Fork, were as a whole remarkably free 

 from pearly growths or discolorations. Occasional individuals from Maho- 

 met, on the Sangamon River, have round, pin-head pearls in the shell. 

 Though no distomids were observed in the animals of luteola it is quite 

 probable that these pearls and blisters, which were observed for the most 

 part in empty shells, were caused by distomid larvae, possibly the mar- 

 ginal cyst described by Wilson and Clark (1912:62). Many young shells 

 of luteola were collected and many more observed, indicating that the 

 species is breeding freely from the Homer Park section of the stream down- 

 ward. No young shells were seen above the Homer Park dam. Gravid 

 females were observed at several places in September and October. 



A specimen collected at Mahomet (Z11223 A) somewhat resembles 

 Actinonaias ligamentina in the form of the shell, absence of strong umbonal 

 markings and heavy hinge teeth; it seems to be one of those individuals 

 which has led many students to say that ^^ligamentina runs into luteola.'^ 

 The shell is free of all abnormalities and has a clear pearly-white nacre. 

 It measures, length 87, height 54, breadth 30 mm. 

 33. Lampsilis ventricosa (Barnes). Pocket-Book. 



This large fine species was not collected in Salt Fork above the station 



about two miles north of Sidney, 16 miles below Urbana. As it does not 



occur in Spoon River (as far as known from our collections) it is probably 



a species that does not inhabit the smaller tributary streams. From the 



station mentioned as far down stream as the river has been examined, 



including Middle Fork, ventricosa is common or abundant in most places. 



Below Homer Park dam it is abundant and of large size, and more or less 



ponderous. The largest female shell was found at Homer Park and the 



largest male shell in Salt Fork near Middle Fork. These shells measure as 



follows: 



Length, 138; height, 60; breadth. 56 mm. Male 

 " 117 " 60 " 60 mm. Female 



