JEFFERY: THE MOLLUSCA OF WESTERN SUSSEX. 311 



slime (byssus) and so rise perpendicularly to the surface, 



and having taken the required supply of air, turn 



leisurely about and crawl down the same web again. 



Once while witnessing this performance, the slime 



parted from its mooring, when poor hypnorum was 



quickly carried to the surface again by the air which it 



had taken in. 



Both species of Physa have beautifully polished 



shells, which of course would soon become covered with 



conferva,- &c., if not kept off by some means. This 



office snails often perform for each other by rasping with 



their liorny jaws in the usual operation of feeding, but 



P. hypnorum can effect this for hself unaided, even to 



the very point of its long shell, as I have had proof by 



observations on some I kept in an aquarium. 



P. fontinalis. Generally distributed: often found in deep water. 



Limnsea peregra. Common : the varieties ovata and 

 acuminata occur. 



L. auricularia. Occurs in some artificial ponds in my garden. 



L. auricularia var. ampla. Artificial ponds in my garden. 



L. stagnalis. I found this species for the first time in the 

 Burpham brooks (levels of the Arun) last summer (1881). 

 Mr. Harting in his "Mollusca of Sussex," Zoologist, 

 1878, writes that it is "common in ponds and ditches," 

 but it certainly is not found near Chichester. 



L. palustris. Common: I have obtained the variety elongata 

 from Freshwater in the Isle of Wight. 



L. "truncatula. I think this species has a better claim to be 

 called the 'wandering' mud shell than Z. peregra, for 

 wherever a roadside stream trickles down in spring it is 

 sure to find its way, no matter to what elevation and 

 almost equally certain to be dried up in summer. 



