BULLA DIPPER. 77 



somewhat striated, and rather wrinkled longitu- 

 dinally, with two or three faint tranverse ridges 

 on the body whorl. Length in the largest 

 specimens, half an inch, breadth a quarter. 



This is a British species, not unfrequently 

 found in stagnant pools and running waters, upon 

 the under side of the leaves of aquatic plants. 



The animal is of a light yellowish colour, has 

 two long setaceous* tentacula, with two black 

 eyes placed underneath at their base. When in 

 motion, it covers great part of the shell with a 

 transparent membrane, scarcely perceptible to 

 the naked eye. 



It has very considerable powers of locomotion, 

 and transports itself with the shell downwards, 

 by adhering to the surface of the water, crawling 

 over it with as much apparent ease as if it were 

 on a solid body. It can also let itself down 

 gradually by a thread which it affixes to the 

 surface of the water, as a caterpillar attaches 

 itself to the branch of a tree ; it is the only 

 animal that is known to be capable of thus sus- 

 pending itself under water. It has also the 

 power of throwing its shell about in an extraor- 

 dinary manner, whilst it keeps its body fixed by 

 its foot ; it probably resorts to this singular 

 habit either in self-defence, or to remove the 

 little aquatic animals with which it is tormented. 



* Setaceous "bristle shaped, from Latin seta, a bristle. 



