154 College of Forestry 



stagnalis lilliancc, Acella haldemani, Planorbis Irivolvis, Fla- 

 norbis trivolvis fallax, and Segmcntina armigera. It will be 

 noted in Table No. 44 that certain depths appear to be the limit 

 for some species and the beginning for others. Thus at eight 

 feet, six species drop out and six species appear, while at nine 

 feet, four additional species disappear. Two species seem to 

 be confined to water deeper than ten feet, Amnio ola emarginata 

 and Valvata sincera. 



The variation in distribution of certain species is interesting. 

 Lanipsilis luteola occurs at all depths beyond three feet. 

 Lampsilis radiata occurs in water up to three feet in depth 

 but its race oneidensis does not appear until a depth of eight 

 feet is reached. Anodonta implicata appears to be restricted 

 to water less than four feet deep while its relative, Anodonta 

 grandis footiana, occurs down to 15 feet. The mussel Elliptio 

 is found at all de'pths and on all kinds of bottom. Sphcerium 

 vermontanum extends from one and a half to 14 feet but its 

 congeners sidcatiim and solididimi do not appear until a depth 

 of eight feet is reached. Muscidinni disappears at eight feet 

 but Pisidium extends to 14 feet. Goniohasis and Cmnpeloma 

 are shallow water genera (four to five feet) while Gillia and 

 Somatogyrus persist to a depth of 14 feet. Valvata tricarinata 

 is found at all depths but its relative Valvata sincera does not 

 appear until a depth of 12 feet is reached. Amnio ola bakeriana 

 and allied species occur at nearly all depths but Amnio ola 

 emarginata first occurs at a depth of 10 feet. Amnioola lus- 

 trioa was not found in water deeper than three feet. Of the 

 wheel-snails, Planorbis, seven species occur at three feet, five 

 species at nine feet, two species at 14 feet, and but one, Pla- 

 norbis antrosus, is found at 18 feet. Physa is a shallow water 

 group, living in water one to three feet deep when adult, but 

 occurring as deep as 11 feet when young. The disappearance 

 of the fresh- water limpet, AncyluS parallelus, at 11 feet is due 

 probably to the absence of suitable vegetation wdiich is scanty 

 or wanting at this depth. The paucity of plants at this and 

 greater depths is probably one of the reasons for the diminish- 

 ing number of species as the water deepens. 



