152 



POPULAR CONCHOLOGY. 



painted with various colours in rays from the apex to the 

 margin. Forbes says that the very young shells do not 

 have the apex perforated, the opening being lower down. 



Deridobranchus. Ehrenberg. — Animal like a shell- 

 less Emarginula ; the mantle forms over the front a fold, 

 covering the two symmetrical comb-shaped gills, and there 

 are a pair of tentacula bearing the eyes at the base. — 

 1 species. 



D. argus is found in the Red Sea. 



Order III. 



CYCLOBRANCHIATA. 



The animals of this order are symmetrical, and have the 

 organs of respiration placed in a circle round the body, in 

 the form of little leaves. The families Patellacea and 

 Chitonacea, which belong to this order, agree apparently 

 in the internal organisation, however they may differ ex- 

 ternally ; their enormously long tongue is similarly armed, 

 the middle line has several rows of teeth, and the sides 

 several rows of hooks ; the Patellacea have tentacula and 

 eyes, and the heart is placed in front, whilst the Chitonacea 

 have no tentacula nor eyes, and the heart lies behind. 



Family l. — PA TELL A CEA. 



Animal with tentacula and eyes ; the heart placed in 

 front. The shell is mostly of a shallow cone-shape. — 

 Marine. 



Patella. Lin. (Lepas Adan. ; Goniclis Rqfin.) — 

 Shell simply conical, not spiral ; without any perforation, 



