INDIAN PHORUS. Phorus 'Indicus. 



STAIRCASE OB PERSPECTIVE TROCHUS. Solarium perspectivum. 



not very particular about this drawback, neither is the thrush, which, in winter, when the 

 snails are hidden away in their dark recesses, finds a meal easier to be obtained on the 

 sea-shore than in hunting for its usual prey. 



ONE of the prettiest members of this family is the WINDING STAIRCASE-SHELL, or 

 PERSPECTIVE TROCHUS, so named on account of the peculiar formation of its whorls. 



If the shell be held with its top downwards, it looks exactly as if it had been 

 wound around a conical centre which had afterwards been withdrawn, and the projecting 

 edges of the whorls have a wonderful resemblance to the perspective view of a winding 

 staircase seen from below. 



Perhaps the most remarkable point about this genus is the singular operculum of some 

 of the species, which differs from that of any other mollusc. Instead of being a nearly 

 flat plate of horny or shelly substance, it is a conical structure of shelly matter with a 

 riband of membranous substance wound round it, and projecting like the mechanical 

 form so well known as Archimedes' screw. The object of this singular variation is 

 quite unknown. 



The colour of the shell is rather variable, but consists of mottlings with brown, ochre, 

 and white. 



A VERY curious member of this family is the LOOPING SNAIL ( Truncatella truncdtula), 

 a little species that is remarkable for the habit which has earned for it its popular name. 

 All these creatures inhabit the space between tide marks, and can live for many weeks 

 without water. Their mode of progression is very peculiar, and closely resembles that of 

 the leeches or looping geometric caterpillars with which we are so familiar. When they 



