THE NAUTILUS. 137 



Length 25.0; breadth 4.0; aperture length 10.0; breadth 

 2.25 mm. 



Length 25.0; breadth 4.0; aperture length 10.0; breadth 

 2.0mm. 



Length 23.0; breadth 4.0; aperture length 10.0; breadth 

 2.5 mm. 



Adults are said by Kirkland to appear in Reed's Lake, Mich- 

 igan, about September 25 and to be common until Thanksgiving 

 Day or later. They were observed in the west end of Oneida 

 Lake, in several places, on September 10 and continued to be 

 noted until the middle of October, when they were quite abun- 

 dant. At this time work was discontinued by the writer. 1 No 

 adults were seen in July, 1916, at which time several of the 

 habitats were visited in which Acella was abundant in the fall 

 of the previous year. It is evident, from the observations of 

 Kirkland, Sargent, and the writer that Acella migrates to deeper 

 water sometime in the late 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 so cold 

 that it numbed the fingers, in fact ice had formed the morning 

 of the same day. 



Acella is purely an inhabitant of vegetation, at least as far as 

 the recorded observations indicate, and as far as known has 

 never been found on any other material. Kirkland and Sargent 

 note it on the under side of lily leaves. In Oneida Lake it has 

 been noted on the following vegetation : 



Smith's bullrush (Scirpus smithii) on the stem. 

 Floating pond-weed (Potamogeton natans~) on leaves and stem. 

 Pond-weed (P. interruptus) on leaves and stem. 

 White water-lily (Castalia odorata) on leaves and stem. 

 Yellow water-lily (Nymphaea advena) on leaves and stem. 

 The habitat in Oneida Lake is invaribly a sheltered cove, bay, 

 or other spot protected from violent wave action. 



1 Baker, Technical Bulletin, N. Y. State College of Forestry, IV, pages 

 283-284, 1916. There are also other references to the ecology of the species 

 in other parts of the volume. 



