149] FAUNA OF BIG VERMILION RIVER— BAKER 51 



some of these Rafinesquean names have not been adopted too hastily and 

 whether the fact of the identified specimens in the Poulson collection has 

 not unduly influenced the references, which, without these identifications, 

 are not as clear. The test must be, it would seem, a clear case of identifi- 

 cation from the writings of Rafinesque alone. 



30. Eurynia (Micromya) lienosa (Conrad). 



The distribution of this small mussel seems to be coincident with that of 

 Lampsilis luteola in the Big Vermilion and its tributaries. It occurred 

 infrequently living in the Spoon River. It was not again collected in a 

 living condition above the iron bridge north of Sidney, seven miles below 

 Spoon River. At this place only one living specimen was found, and as 

 far down as the cement bridge it is only infrequent. Between this point 

 and the station three and a half miles above Homer Park dam no living 

 specimens were found after diligent search in favorable habitats. It does 

 not occur in any abundance above Homer Park dam; but below the dam 

 the species is abundant and of large size. The largest specimens from 

 Homer Park measure: length, 65; height, 31; breadth, 28 mm. (male); 

 length, 55; height, 34; breadth, 25 mm. (female). In Salt Fork near its 

 junction with Middle Fork it is abundant and in the Middle Fork it is 

 common. 



The species varies somewhat in coloration. From Homer Park up- 

 stream the color is black or dark brown with rarely faint indications of 

 rays. Specimens from Middle Fork and Salt Fork near Middle Fork are 

 more of a chestnut color, slightly reddish, often with quite distinct rays. 

 By arranging the different lots by consecutive stations down the river it 

 may be at once observed that there is a marked and striking increase in 

 size, the increase being in some cases as much as 50 percent between Spoon 

 River and Homer Park. The Homer Park shells are on the average some- 

 what larger than those from farther down the stream and from Middle 

 Fork. 



The shells of many individuals of this species contain pearly growths 

 in the form of blisters and 'pin-head' pearls. These occur near the margin 

 of the valve, more frequently near the posterior end near the siphonal 

 region. Gravid females were collected at Homer Park on July 30. 



Lienosa was not collected from the Sangamon River and no records 

 have been seen of its occurrence in that stream. 



31. Eurynia (Micromya) iris (Lea). 



A broken valve of this species was found in Middle Fork below the 

 interurban bridge. The rays are distinct and the shell seems typical. 

 It measures, length 37, height 21 mm. It appears to be a very rare shell 

 in the parts of the Big Vermilion examined but may be more abundant 



