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. 



