145] FAUNA OF BIG VERMILION RIVER—BAKER 47 
found after careful search; in one place, below the first bridge south of St. 
Joseph, dead, empty shells were abundant, but a careful search, conducted 
on two days, failed to discover a single living specimen. The largest and 
finest shells occur at Homer Park on a mud bottom in water from two to 
three feet deep. The largest shell from this station, a female, measured: 
length, 185; height, 130 mm. The species was observed to be gravid on 
the 6th of November, in 1918, and on October 8, in 1920. 
The shells of complanata are very uniform in general shape, nacre, and 
condition. Pearly growths or pathological forms are rare. A few specimens 
contained small pin-head pearls and an occasional individual had suffered 
slight injury to the posterior part of the shell. The presence of many young 
and immature specimens indicates that the species is now breeding well 
and that the glochidia are finding suitable fish hosts. Young shells from the 
Sangamon River, where the species is abundant, are more of an olive color 
and not as green as those from the Salt Fork and other parts of the Big 
Vermilion River. Old shells from both drainages are dark brown or black. 
22. Alasmidonta (Pressodonta) calceola (Lea). 
This species has been recorded by Mr. Zetek from west of White Heath 
in the Sangamon River. No specimens were observed during the recent 
survey. As far as known it does not occur in the Big Vermilion River. 
23. Alasmidonta (Rugifera) marginata Say. Elk-Toe. 
In the big Vermilion River, this species is found, infrequently, at most 
stations from bench mark 655 as far down as the stream has been examined. 
It is not abundant anywhere and common at but three stations—below 
the dam at Homer Park, south of Muncie, and in the Big Vermilion. The 
first station where living specimens were found is four miles above the 
Homer Park dam. Individuals, both above and below the dam, are of 
good size and fine color, the characteristic green rays being very brilliant. 
Specimens from Middle Fork have many black spots on the shell. The 
largest specimen collected from the station two miles above the Homer dam, 
measured 80 mm. in length and 45 mm. in height; one from the Big Vermil- 
ion measured 96 mm. in length and 48 mm. in height. 
Marginata exhibits little evidence of parasitism or abnormalities. One 
specimen collected from two miles above the Homer dam had several 
pearly growths and blisters indicating distomid infection. Gravid females 
were collected on October 8 and 13, 1920. 
This species is rare in the Sangamon River, only one specimen being 
found at Mahomet during a days search. Marginata is a species more com- 
mon in the upper waters of rivers and streams and is not, as a rule, found 
in any number in the larger rivers. 
( 
