155] 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. 
tf 90 eee All “33mm. 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. Amodontoides 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. Trunciila (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 male and largest female shell measure as follows, eorre- 
sponding measurements being also given for the Alabama shells. 
Length, 41; height, 29; breadth, 22mm. Danville, male, Z3770. 
at sai 34: “20mm. Danville, female, Z3770. 
oe bs) soe) «43 “32 mm. Alabama male, Z3947. 
eer i dE} «35mm. 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 
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