TESTACEA. 27 



This work does not profess a scrupulous adherence to the particular 

 point of arrangement. It is rather devoted to the discussion of habits, at 

 least it is so in a great measure, than to minute descriptions of the forma- 

 tion of parts. While the latter has been attended to by others, the 

 former has been greatly overlooked and neglected. 



At the same time, a general correspondence in the form of all the 

 animals brought together in sections, is carefully observed here ; there- 

 fore none which are thus approximated can be in fact very remote. 



Ancylus fluviatilis. — Plate VI. 



The habits of this animal bear great similarity to those of the limpet, 

 so common on the I'ocks and stones of the sea-shore ; but it is an inhabi- 

 tant of the fresh- waters. 



Probably its name, Ancylus, originates in the presumed resemblance 

 of the shell to a particular kind of shield known among the ancients. It 

 seems to have been first given by Geoffroy, and afterwards recognised or 

 adopted by MiiUer, Historia Vermium, vol. ii. p. 199. 



Length of the shell three or four lines ; height above two ; form of 

 the circumference a broad oval. The apex, slightly curved, is situate 

 nearer to the posterior than to the anterior extremity. Colour tending 

 to olive ; apex brown. Animal a Limax, or apiiroaching that genus, of 

 about the same length as the shell ; body broad, head large and distinct, 

 with the mouth conspicuous below ; tentacula two, with a very black eye 

 at the internal root of each ; colour slate-grey. 



This creature is endowed with considerable activity. The sole, in 

 crawling, extends somewhat beyond the margin of the shell ; and in 

 passing over an angular substance, the body, relieved from the sides of it, 

 then seems attached exclusively by that portion of the flesh forming the 

 highest part. 



The animal feeds on the confervoid aquatic plants vegetating on stony 

 .surfaces ; also on wood, as decaying branches, and on other substances. 



