THE NAUTILUS. 



87 



Amnicolidae. 



Gillia altilis (Lea). Occurs on boulder, gravel, sand, and 

 mud bottoms in water 1-14 feet deep. Half-grown and adult 

 individuals were abundant in some habitats. 



Somatogyrus subglobosas (Say). A few specimens were col- 

 lected associated with Gillia. All were immature. 



Bythinia tentaculata (Linn.). This common species occurs 

 abundantly in Lower South Bay on gravel, sand, clay, and mud 

 bottoms in water 1-14 feet deep. Most abundant on clay 

 and mud bottoms in water 4-14 feet deep. A large percentage 

 of the individuals collected were young or immature. This 

 species is especially abundant in filamentous algas (mostly Cla- 

 dophora fracta) and a single specimen was collected from a leaf 

 of the arrowhead, Sagittaria arifolia. A pint of alga?, represent- 

 ing 100 square inches of area on an old log in 5 feet of water, 

 yielded 97 adult and 1270 young individuals of this species. 



Amnicola limosa porata (Say). This is the largest Amnicola 

 in the lake, and was found only in three habitats: boulder bottom 

 in one foot of water, sand bottom in four and a half feet, and 

 mud bottom in 18 feet of water. It was most abundant on a 

 rocky shoal in water a foot deep, a single boulder having 54 

 specimens. Typical limosa is apparently not found in this part 

 of the lake. 



Amnicola bakeriana nimia Pils. 1 This is the most abundant 

 Amnicola in the lake, easily known by its wide swollen shell. 

 It occurs on all kinds of bottom in water from 1-18 feet deep; 

 about 10 per cent of the material collected was immature. Most 

 abundant, as are all of the species of the genus, in filamentous 

 algae. A single specimen was found on the leaf of Sagittaria 

 arifolia. 



Amnicola bakeriana Pilsbry. One of the most abundant species 

 in the lake easily recognized by its long spire and deep-sutured 

 whorls. It occurs on all varieties of bottom, though least 

 numerous on boulder and most numerous on clay and mud 

 bottoms where there is a heavy growth of algae. In depth it is 

 most abundant in water from 3-6 feet deep, and occurs from 



Nautilus, xxxi, pp. 44-46, 1917. 



