﻿Notice of Dr. MantelFs Medals of Creation. 125 



inhabited these elegant and enduring structures ; even those so 

 commonly eaten (as for example oysters and clams) are regarded 

 as shapeless gelatinous masses,* yet they are the very beings that 

 secreted and formed the lustrous and symmetrical shells, and 

 are indeed objects of the highest interest to the naturalist. 



" To the geologist, from their permanent nature and the proofs 

 they yield of the conditions under which the strata that contain 

 them were deposited, they are important in the highest degree ; 

 and geological formations have been classified from the shells 

 they contain, and from their numerical proportion in different 

 groups of strata ; witness the Eocene, Miocene, and Pliocene of 



Mr. Lyeli." 



The Gasteropoda {feet under the body) are very widely dis- 



tributed. The garden snail is a familiar example of a terrestrial 



Gasteropod. 



Among the Cephalopoda {feet around the head) the cuttle 

 fishes have no shell but an internal skeleton or sheath ; in all 

 the other mollusca the head parts are external. Some of the 

 mollusca have a retractile prohoscis armed with minute teeth, by 

 which they can rasp or bore into the shells of the species on 



which they prey. 



The number of known living mollusca exceeds 6,000. 



" The Pectens, unlike the oysters, have the power of locomo- 

 tion, and may be seen moving with rapidity, and napping their 

 shells to and fro with great activity. Numerous species are 

 found fossil." "Of the Conchifera, or bivalve shells, nearly 

 800 species are known in Great Britain." 



The Gasteropoda have a head and mouth, with jaws, eyes, 

 and feelers ; and they generally creep by means of a fleshy disk 

 or foot, which is situated under the belly. The greater number 

 are marine, but some live on trees, or in rivers or streams, or in 

 stagnant and brackish waters. The common snail, river snail, and 

 periwinkle, are instances of terrestrial, fluviatile, and marine forms. 



The number of Gasteropods in the British strata is nearly 800, 

 distributed through the sedimentary formations from the Silurian 

 to the newest tertiary, in which the greater proportion is found. 

 Dr. Mantell has given the name of molluskite to a dark matter 



* " You shapeless nothing in a dish, 

 You that are hut almost a fish." 



Cowper's Oyster and Sensitive Plant. 



