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GEOIvOGY OF LA SAI^TvE COUNTY. 115 



Varies in shape, but its obliquity is constant. Its 

 peculiarity is the apex of the beaks, which assume the 

 appearance of wings placed on the summit of the 

 umbones. The animal is active. Other species of 

 this famil}^ are reported from Illinois, but I am unable 

 to report more from this county. S^h. striatimim, 

 Lam., if a distinct species should be included, as we 

 have the shell. The Sphceriiims are sometimes mis- 

 taken by local observers for youno- Uniones. 



The Uniones or Naiades are a genus of fresh 

 water mollusks found in most rivers and lakes, and 

 common to the streams of both warm and cold climates. 

 It is a very extensive genus, containing more than 

 1,200 admittedly distinct species, and some of these 

 furnishing several varieties. The shells are generally 

 white, buff, brown, -black, green, yellowish green, 

 or variegated with these colors; they are smooth, 

 warty or spinous, and while some are very thick and 

 heavy, others are thin and fragile. They also differ 

 greatly in size, some when full grown attaining a 

 length of eight to ten inches, others not more than two 

 and a half to three inches. The shells are smooth 

 inside, and vary in color from pearly white through 

 bluish white to salmon and purple. 



The Unio belongs to the class acephala or headless 

 mollusks, that is these animals have no well defined 

 head, order Lamillibranchiata, having gills made up 

 of several thin layers or lamella. They are called 

 bivalves because the shell is composed of two pieces or 

 valves united by an elastic gristle and teeth usually 

 two on one valve, and one on the other, which interlock 

 and are usually thick and short. One end of the shell 

 is larger than the other, ani this is called the anterior 

 or forward end, the other the posterior or hind end. 



