125] FAUNA OF BIG VERMILION RIVER—BAKER 27 
pression of the shell, for all live in the same section of the stream under 
identical conditions. The rule cited by Ortmann, however, seems to be 
applicable in most cases. 
Several species increase in size toward the lower part of the river. This 
is especially true of Anodonta grandis, Strophitus edentulus, Alasmidonta 
marginata, Eurynia lienosa, Lampsilis luteola, Amblema undulata, and 
Lampsilis ventricosa. A few others show some increase at different stations. 
One species, Uniomerus tetralasmus, is apparently confined to the upper, 
smaller tributary streams of Salt Fork. It was common in the ditch north 
of Urbana; in Crystal Lake, Urbana, in Spoon River; and at Muncie in a 
small tributary. Two broken valves were found at the station called the 
natural dam, but these are believed to have been washed into this stream 
from a nearby tributary which was dry when this part of the Salt Fork 
was examined (September 25). Tetralasmus probably also occurs in the 
TaBLe VII. Variation oF Fusconaia Rubiginosa 
Length Width Per cent Station No. Distance from 
Urbana 
58 23 39 17 1514 miles 
62 26 42 AcleNne 5 “adaauaas 
61 ol 50 Sam” | esaaae violate 
68 27 39 a0) © eee (osnoGodee 
79 33 42 see NS eee Sects 
86 33 38 24 2434 miles 
89 41 46 Aol We Scacatons 
90 31 34 25 27 miles 
82 35 42 SDuk ll mopEnsconp 
89 47 52 COPR Peal bazccyscmaci 
71 30 42 26 36 miles 
67 30 44 coe Opera ston 
102 41 40 30 46 miles 
65 30 46 bce ll ee pocEotrns 
86 43 S0lS Be PSS ike ad eee 
streams have not been examined. The majority of the other species occur 
at several stations along the Salt Fork and its tributaries and no particular 
variation in distribution was observed except as already noted. 
Three mussel species and varieties were found in Crystal Lake that 
are exotic as far as the Big Vermilion River is concerned. These are Ano- 
donta grandis gigantea, Anodonta corpulenta, and Uniomerus tetralasmus 
sayit. These species were artificially introduced into this body of water 
about 1908 by a member of the zoological department of the University of 
Illinois. They originally came from a stream in western Indiana. That 
these mussels found a favorable environment and have thrived during these 
years is evidenced by the number of fine specimens recently collected when 
the lake was partly drained. Only the Uniomerus was rare, but one speci- 
men being found. As Crystal Lake is not connected with the Salt Fork 
