SEA-SNAILS AND SEA-SLUGS. 221 



Pheasant shells (Phasianella pullas), that have the misfortune 

 to be so small, or they would be greatly esteemed for their 

 rich colouring. They are very smooth, and of a white or pale 

 yellow hue, but so thickly covered with fine crimson lines that 

 at first sight this appears to be the colour of the shell. These 

 lines run parallel with each other, but with many curves, some 

 flowing gently, others short and acute. These lines vary much 

 in thickness throughout their length, here being very fine, there 

 thickening gradually and thinning off again. The shells are 

 less than a quarter of an inch in length, and the mouth is 

 closed with an operculum. The animal has the peculiar habit 

 of moving first one half, then the other, of its foot in pro- 

 gressing. 



One of the handsomest of our common rock-shells is the so- 

 called Common Top (Trochus zixyphinus), though it is scarcely 

 as plentiful as the much smaller Grey Top (Trochus cinereus). 



THE COMMON TOP. 



It is pyramidal in form, with an almost flat, broad base; 

 the mouth closed by a spiral, horny operculum. In some 

 species there is an umbilicus, in others it is wanting. The 

 animal has two small fringed lobes between the tentacles, 

 and similarly fringed lappets to the neck. The sides, too, are 

 lobed, and several tentacle-like processes are given off from 

 them. 



