BULLA DIPPPER. 79 



produced ; aperture oval oblong, three fourths 

 of the length of the shell. Old specimens are 

 somewhat striated, and rather wrinkled longitu- 

 dinally, with two or three faint transverse ridges 

 on the body whorl. Length 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 on a 

 solid body. It can also let itself down gradu- 

 ally by a thread affixed to the surface of the 

 water, as a caterpillar does from the branch of a 

 tree ; it is the only animal that is known to be 

 capable of thus suspending itself under water. 

 It has the power of throwing its shell about in an 

 extraordinary manner, continuing, at the same 

 time, fixed by its foot. It 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. 



