137] FAUNA OF BIG VERMILION RIVER—BAKER 39 
the first two places it is very rare, only a few individuals having been 
found by Professor Smith in a number of years. In a days search at 
Homer Park by two experienced collectors, only two living specimens and 
odd valves of two others were found. The largest specimen from Homer 
Park measures 72 mm. in length and 63 mm. in height. This species is one 
of the most abundant of shells in the Big Vermilion below Middle Fork, 
where specimens measuring 100 mm. in length are common. The distri- 
bution of this species is a good example of the progressive development of a 
species in the downward course of a stream, for in the course of about 
twenty miles the size nearly doubles. Beginning as a rare form at Homer 
Park it becomes one of the most common forms in the Big Vermilion, 
twenty miles downstream. 
All of the Big Vermilion tuberculata are of the compressed type, and 
the shell is covered posteriorly and ventrally with large tear-like pustules. 
The anterior third of the valve is free from pustulation. The nacre of all 
shells seen is rich purple, which renders the species valueless for the button 
makers. Yuberculata does not occur in the portions of the Sangamon River 
examined. 
11. Elliptio gibbosus (Barnes). Lady-Finger; Spike. 
This mussel does not occur in Salt Fork, nor in any tributaries of the 
Big Vermilion above Danville that have been examined. It is fairly com- 
mon in the Sangamon River at Mahomet on a sand and gravel bottom. 
Young and immature shells are distinctly rayed. The nacre of all speci- 
mens examined has been purple, no white-nacred individuals being seen. 
In the Kankakee River white-nacred specimens occur and become the 
dominant form in the lower part of the stream (Wilson and Clark, 1912:45). 
In the Illinois River beds of shells occur which have either a white or a pur- 
ple interior. (Danglade, 1914:42). This familiar shell will probably have 
to be known as dilatatus (Rafinesque) if the original description is definite 
enough to identify it as the gibbosus of Barnes. Dilatatus was described 
in 1820. It is a pity that these names of Rafinesque could not have been 
applied earlier to these shells and thus saved the confusion which is now 
resulting from the changes of the old familiar names which zoologists in 
our universities have used for years in connection with their classes in 
systematic zoology. 
12. Uniomerus tetralasmus (Say). 
This species has been found living only in the upper waters of Salt 
Fork and in Stony Brook near Muncie. It occurs in fair numbers in the 
stream above Urbana and in Spoon River. Two broken valves were found 
in Salt Fork at the station called natural dam about 12 miles below Urbana. 
No living mussels could be found in the stream at this point and it is 
believed that the odd valves were washed into Salt Fork from a small 
( 
