The Productivity of Fish Food in Oneida Lake 179 



able from the observations of Kirkland, Sargent, and the writer 

 that Acella migrates to deeper water by crawHng down the 

 stem of rooted vegetation (Potamoc/eton, Scirpns, etc.) some- 

 time in the fall or early winter, probably when ice forms to 

 such an extent that the surface vegetation upon which it rests 

 and feeds is destroyed. That it will resist cold weather is 

 shown by the observations of Kirkland, who found it on 

 Thanksgiving Day when the ice had formed, and by the writer, 

 who collected it in October when the water was covered with 

 a thin film of ice in the early morning (Baker, '17, p. 135). 



Oenus Galea Schrank 



87. Galba catascopium (Say). 



One of the most abundant of Oneida Lake mollusks, found 

 on all varieties of bottom in water one-half to 14 feet deep. 

 It is most abundant on sand and mud bottoms when young and 

 on boulder and gravel bottoms when adult. This pond-snail 

 occurred at nearly all habitats but the majority of the indi- 

 viduals were very young, measuring 3 to 7 mm. They were 

 usually associated with filamentous algae {CEdogonium, Clado- 

 phora, or Spirogyra) . Catascopium apparently changes its 

 habitat with age, the young living among algse on a mud, clay, 

 or sand bottom, frequently in comparatively deep water (14 

 feet), while the adult lives usually on a boulder or gravel 

 bottom in shallow water (one to three feet). 



A single specimen was collected near Norcross Point on a 

 sand bottom in three feet of water. The spire is very short 

 and broad, the inner lip is broad and reflected over the vimbili- 

 cal region completely closing the umbilicus. The specimen 

 measures: length 6.50, breadth 5.00, aperature length 4.50, 

 breadth 3.00 mm. The shell is an exact duplicate, in miniature, 

 of a form of Galba emarginata mighelsi from Maine, such as I 

 have figured (Baker, '11, pi. 41, fig. 25). It is a case of 

 ]>arallel development. 



88. Galba emarginata (.Say). 



This species was not detached in the 1916 collections. It 

 was collected in 1915 (Baker, '16, p. 285) on a bouldery poin!; 

 or in a sandy, expcsed bay. While collecting in the fall of 

 191 7 the species was again encountered on the bouldery shores 



