155J FAUNA OF BIG VERMILION RIVER— BAKER 57 



lowish shell with little or no indication of rays. Middle Fork specimens 

 include yellowish shells without rays, as well as, more rarely, individ- 

 uals with rather bright, wide rays, approaching in this respect the 

 related species fallaciosa of Simpson. The largest specimens from the 

 two localities measure as follows: 



Length, 124; height 57; breadth 47 mm. Male, Homer Park. 



90 " 41 " 33 mm. Female, Middle Fork. 



The nacre is tinted with pinkish or salmon color. Pearly growths 

 are not uncommon in specimens from the Big Vermilion. These are 

 in the form of blisters and pin-head pearls, which are usually confined 

 to the margin of the shell between the pallial line and the external margin 

 of the valve. One individual from Homer Park had the entire area between 

 the pallial line and the ventral margin of the shell abnormally enlarged 

 and thickened, due possibly to the presence of distomid larvae and to some 

 extent to the intrusion of small amounts of soil between the mantle and 

 the animal (Z11147A). Specimens from Middle Fork are, as a rule, 

 free from pearls and abnormal growths. Gravid females were found on 

 September 26 in Middle Fork, and on July 30 in Salt Fork at Homer 

 Park. Anodontoides has not been recorded from the Sangamon River at 

 Mahomet or in the other places examined. 



The early writers. Say, Conrad, and others, have identified this species 

 with the Elliptio teres of Rafinesque (1820) and if the shell is clearly identi- 

 fiable from the description of Rafinesque the familiar name of Lea must 

 become a synonym. 



36. Truncilla (Pilea) perplexa rangiana (Lea). 



Four specimens of this race of perplexa are in the naiad collection 

 of the Museum of Natural History, University of Illinois, collected 

 by Mr. A. A. Hinkley, in the Big Vermilion River at Danville. Three 

 are females and one is a male. They are much smaller than specimens 

 from Florence, Alabama, where the species attains its greatest develop- 

 ment. The miale and largest female shell measure as follows, corre- 

 sponding measurements being also given for the Alabama shells. 



Length, 41; height, 29; breadth, 22 mm. Danville, male, Z3770. 



" 44 " 34 " 20 mm. Danville, female, Z3770. 



" 55 " 43 " 32 mm. Alabama male, Z3947. 



" 73 " 53 " 35 mm. Alabama female, Z3947. 



As no specimens of Truncilla were found in the Big Vermilion or its 

 tributaries as far down as Middle Fork, which is but a few miles west 

 of Danville, this species evidently does not inhabit the stream above the 

 locality from which Hinkley collected his shells. Truncilla perplexa 

 as well as its variety rangiana is known in Illinois only from the Ohio 



