1 56 INTRODUCTION TO ZOOLOGY. 



wanting, presents great diversity in position and figure, and 

 is, in some species, a very remarlcable and attractive object. 



Tlie Mollusca are very widely diffused, abounding not only 

 in tropical and arctic seas, but in lakes, ponds, and rivers. 

 Some, round our coasts, are found buried in sand or mud ; 

 others construct their dwellings in indurated clay, and even 

 in limestone rocks. Some species {Fig. 147) delight in quiet 

 Buimy nooks, on the margin of fresh- water pools; some in 

 rapid and mighty rivers; and others dwell in the ocean at 

 depths which have been but seldom explored by the dredge 

 of the natm-alist. But though the greater number are aquatic, 

 all are not so. The terrestrial species, even in our own 

 country, are found in oui* pastures, our gardens, and our 

 plantations ; some may be found on sandy banks, others in 

 moist and shady places ; some lurking under witljcred leaves, 

 and others at various heights on the trunks of our forest trees. 



Fig. 148.— BucciNDM. Fig. 149.— Volcte. 



The beautiful variety of form {Figs. 148, 149, &c.) ob- 

 servable in the sliells of different species of Mollusca, has, in ail 

 ages, attracted attention ; and the splendour of their colouring 

 is not surpassed by that of our brightest garden-flowers. In 

 some respects it is even superior, for their most delicate tints 

 become here unfading and permanent ; and a peculiar structure 

 of the suiface gives rise occasionally to iridescent hues. 

 Among savage tribes, shells are formed into elaborate orna- 

 ments, and applied to numberless uses. In a part of Africa 

 a species of shell called " cowry" is the current coin. The 

 wampum belts of some of the North American Indians, 

 whether constituting their records or presented to strangers 

 when they enter mto or recognise a treaty of amity, are 



