94 ETON NATUEE-STUDY 



of the shell which it can completely close, so as to exclude any 

 small intruders. One form we have, with a permanent lid on the 

 end of its '"tail" which, as in the case of the periwinkle, makes a 

 perfect door when the animal retires to its shell. This creature 

 dwells in chalky districts, and its method of crawling might well 

 be compared with that of the common snail. Other forms of 

 similar structure, but breathing water and already alluded to as fresh- 

 water whelks (see Chapter XIX), are to be found in ponds and 

 streams, where also many air-breathing snails of various forms 

 abound. 



In fresh water also will be discovered small bivalves shells, 

 which we know as fresh- water cockles, some of the latter being 

 not so big as a hemp seed. 



COLLECTIONS OF SHELLS 



All the shells of these creatures may be easily preserved, 

 and when mounted in glass-topped boxes on cotton wool, 

 produce a very pleasing effect. Boxes should be got, some- 

 what deeper than the largest shell which is to be admitted into 

 the collection. Rough cotton wool may be put into the box 

 so as to form a foundation. A piece of thin pliable cardboard 

 can be cut so that it would easily drop into the box ; round this 

 a piece of fine jeweller's wadding* should be folded so as to leave 

 the smooth surface uppermost, and the whole arrangement laid on 

 the rough material, after which the edges of the fine wadding should 

 be pushed inwards with a pair of forceps or scissors until it is 

 perfectly even. On this the shells, if of fairly large size, are to be 

 laid. Sometimes it is preferable when the shells are very minute 



* See Appendix. 



