382 Shell Life 



about a quarter of an inch. Instead of frequenting 

 watersides it prefers ditches that are dry, and to 

 retire beneath stones, but it is very restricted in its 

 stations so far as they have been discovered in this 

 country. It has been found in north-east Yorks, 

 in GLamorganshire, in Edinburghshire, and in County 

 Cork. 



The hist of these land Mollusca that we have to 

 notice is a very remarkable creature, the solitary 

 British representative of the family Onchidiidce. It 

 is a little-known slug, OncJddieUa celtica, which is 

 found only on the Cornish and south Devon coasts, 

 where little colonies live so near the sea that, follow- 

 ing the ebb and retiring before the flowing tide, the 

 waves break over them without permanently sub- 

 merging them. The young are provided with a 

 shell, but this is afterwards cast ofi^*, and the adult is 

 only covered by a thick warty mantle. In some 

 species some of these warts bear sense - organs or 

 " eye-spots." There is only one pair of tentacles, 

 supporting the eyes. The sexual orifices are widely 

 separate, that of the male under the right tentacle, 

 that of the female at the end of the body. There is 

 no pulmonary chamber as in all the snails and slugs 

 we have been describing, and breathing has to be 

 performed through the skin and the warts on the 

 back. Their food consists of sand — or rather they 

 eat sand in order to digest out the particles of 

 orpfanic matter that have become mixed with it. 

 They are regarded as air-breathing land-mollusks 

 that are reverting to a marine or semi-marine mode 

 of life. 



