44 



HANDBOOK OF SHELLS. 



in common, and then by subdividing these into other smaller 

 groups, and so on. Thus the animal kingdom is divided, first of all, 

 into Sub-kingdoms, then each Sttb-kingdom into so many Classes 

 containing those which have further characteristics in common, 

 the Classes into Orders, the Orders into Families, the Families 

 into Genera, and these again into species or kinds. 



The Mollusca, or soft-bodied animals, of whose protecting shells 

 your collection consists, form a sub-kingdom, and are subdivided 

 into four classes : 



1. Cephalopoda. 



2. Gasteropoda. 



3. Pteropoda. 



4. Lamellibranchiata (or Conchifera). 

 And these again into Families, Genera, and Species. 



The space at our disposal being limited, it is impossible to do 

 more than furnish some general outlines of the different forms. 

 For further details it will be necessary to refer to one of the 

 larger works, a list of which will be found on the last page. 



CLASS I. The CEPHALOPODA (Head-footed) contains 

 those mollusca that, 

 like the common Octo- 

 pus, have a number of 

 feet (or arms) set 

 round the mouth, and 

 is divided into those 

 having two gills. 

 (Order I. Dibranchi- 

 ata) ; and those with 

 four (Order II. Tetra- 

 branchiata). Order I. 

 is again divided into : 

 (a.) Those with eight 

 feet like the Argonaut 

 (or Paper-nautilus, Fig. 

 4), which fable has so 

 Fig. 4. Argonaut*. Argo. long endowed wit h the 



power of sailing on the surface of the ocean, (it is 

 even represented in one book as propelling itself through the 

 air !) and the common Octopus. (If) Those with ten feet, such as 

 the Loligo (or Squid, Fig. 6), whose delicate internal shell so 

 much resembles a pen in shape ; the Cuttle-fish (Sepia, Figs. 5 & 7), 



Bone' 



of Sef>ia offi- 

 cinalis. 



