BULLA DIPPER. 77 



what striated, and rather wrinkled longitudinally 

 with two or three faint transverse 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 locomo- 

 tion, and can walk with the shell downwards 

 in the water by adhering to the surface, and 

 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 ani- 

 mal that is known to be capable of thus suspen- 

 ding itself under water. It has also the power of 

 throwing its shell about in an extraordinary man- 

 ner, whilst it keeps its body fixed by its foot ; it 

 probably resorts to this singular motion either in 

 self-defence, or to remove the little aquatic ani- 

 mals with which it is tormented. 



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



