496 THE AQUARIAN NATURALIST. 



and iridescent shell ; the top-shaped Trochus, circled 

 round with hoops of crimson flame ; the sculptured 

 Rissoa and the stately Murex; Scalaria with its 

 winding flight of stairs ; and Turritella, like a moving 

 spire of matchless tracery carried upon a living 

 church; Cypraea clad in porcelain, and a hundred 

 more, which almost every beach will furnish. 



The "foot/' which constitutes the distinguishing 

 feature of these GASTEROPODS, is a very remarkable 

 organ ; its structure is entirely made up of an in- 

 extricable interlacement of muscular fibres inter- 

 woven in every possible direction. Progression is 

 accomplished by a series of undulations, propagated 

 in rapid succession along the sole, as we are tempted 

 to call it; so that they appear to occupy the whole 

 surface ; resembling in miniature recurring wavelets 

 on a tranquil sea, gently propelling the creature 

 forward in a continuous mariner, gliding, as it were, 

 over any smooth plane. In progression, however, 

 these animals are not restricted merely to crawl upon 

 the rocks, or other solid substances ; many of them 

 can ascend to the top of the water, and use the sur- 

 face as a liquid floor, along which they creep in the 

 same manner as they do on land, with the difference 

 only of having their body and shell in a reversed 

 position, as though they Avere crawling across the 

 ceiling of a room ; many of our native species may 

 be sometimes seen crossing pools upon the shore in 

 this way, but how they manage to perform such a 

 feat is by no means easily explicable. While float- 

 ing in this manner, these living boats occasionally 

 drop suddenly down, suspending themselves by a 



