THE TOP AND THE LIMPET. 601 



all common, and will still bring a good price in the conchological 

 market. 



The Pheasant-shells are now found in great numbers on the sandy- 

 beaches of several shores, being especially plentiful on the coast of 

 Port Western, in Bass's Straits. The high tide sweeps them toward the 

 shore, where they are left by the receding waters, and seek for shelter 

 beneath the masses of seaweed that are always flung on the beacb by 

 the tide. On lifting these sheltering weeds, the Pheasant-shells may- 

 be found crowded together under their wet fronds. They can move 

 with some speed, the duplicate nature of the foot aiding them greatly 

 in progression. 



The well-known Top is one of the most plentiful species of the Brit- 

 ish coasts, and may be found by hundreds either crawling among the 

 seaweeds at low water or flung upon the sands by the tide. The shell 

 of this creature is beautifully pearly, and when the outer coating is re- 

 moved the iridescent nacre below has a very lovely appearance. Jew- 

 ellers and lapidaries employ these shells largely in their art, polishing 

 them carefully and then stringing them together, so as to form brace- 

 lets and necklaces, or affixing them as ornaments to various head- 

 dresses. 



The well-known univalves, so familiar under the name of Limpets, 

 are divided into several families, on account of certain variations in 

 the structure of the shell. The first family is termed Fissurellidie, on 

 account of the fissure which appears either at the apex or in the front 

 edge of the shell. 



All the Limpets are strongly adhesive to rocks, as is well known by 

 every one who has tried to remove one of these molluscs from the stony 

 surface to which it clings. The means by which the animal is able to 

 attach itself with such firmness is analogous to the mode in which the 

 suckers of the cuttle-fish adhere to the objects which they seize — the 

 formation of a vacuum, and the consequent pressure of the atmosphere, 

 being the means employed. The foot of the Limpet is rounded, broad, 

 thick, and powerful ;• and when the animal wishes to cling tightly to 

 any substance, it presses the foot firmly upon the surface and retracts 

 its centre, while its edges remain affixed to the rock. A partial vac- 

 uum is therefore formed, and the creature becomes as firmly attached 

 to the rock as a boy's leathern sucker to the stone on which he has 

 pressed it. 



We now come to the curious family of molluscs appropriately called 

 Chitonidog, or mail-shells, because their shells are jointed together like 

 the pieces of plate-armor. When separated from each other the plates 

 bear a strong resemblance to the joint of a steel gauntlet, and overlap 

 each other in a similar fashion, a thick and strong mantle taking the 

 place of the leather. There are eight of these plates, and all of them 



51 



