90 THE NAUTILUS. 



and on a clay bottom in water two feet deep. The majority of 

 the individuals were young or immature (3-5 mm.) and were 

 frecjuently associated with alga? (Oedogonium, Chnra, Kitclla) or 

 with the higher vegetation. In one habitat they were found 

 on Potamogeton interruptus and Myriophylluin verticillatum. 



rhysa helcrostropha Say? Several young shells (7 mm. long) 

 thought to be this species were found in Tuttle Brook, Chitten- 

 ango Creek. The surface is smooth and shining and the gen- 

 eral slope agrees with shells from Philadelphia which are un- 

 doubted heterodropha. No adult shells were observed. 



ANCYLIDAE. 



Ancylus parallelns Haldeman. This characteristic fresh-water 

 limpet was collected from all bottoms except boulder in water 

 one and a half to 11 feet deep, the greater number occurring on 

 a sandy clay bottom in one and a half feet of water. In this 

 area it is associated with filamentous alga; {Oedogonium, Cla- 

 dophora) but it is usually more abundant on such plants as 

 Nymphsea, Castalia, Typha and Spjargnnium. 



Ancylus fascus Adams. Young individuals of this species 

 were found in one habitat on a sandy clay bottom in one and a 

 half feet of water. 



Ancylus species. A single specimen of Ancylus was found on 

 a boulder bottom in two and a half feet of water. It was sub- 

 mitted to Dr. Bryant Walker who says of it, "I cannot be sure 

 of the species and therefore prefer to leave it with a question 

 until you get more, which would be very desirable. It does 

 not seem to- be any of the more common species." 



Planorbidae. 



Planorbis trivolvis Say. Specimens of typical trivolvis were 

 found in but one habitat, a quiet lagoon on a mud bottom in 

 one and a half feet of ^vater. 



Planorbis trivolvis variet}'. This form of trivolvis, listed in 

 Technical Bulletin No. IV, page 277, was again obtained in 

 1916, on sand, boulder, gravel and clay bottoms in water one 

 and a half feet deep. Ecologically this form of trivohns differs 

 from the tyi>ical form and it would be convenient for it to have 



