50 



POPULAR CONCHOLOGY. 



Most of them can only creep, and even when they swim, 

 it is only a sort of creeping on the surface of the water, on 

 which they suspend themselves by the sole of the foot, body 

 downwards ; a few only can swim, or float, as Janthina ; 

 some never change their habitats, but remain fixed to one 

 spot, as the Patella, the foot of which, in time, eats a 

 hollow in the rock on which it is fixed ; others are attached 

 by their own shells, as Magilus and Vermetus. The 

 Stylina lives parasitically in sea eggs and star-fish. 



A satisfactory classification is not yet possible, as many 

 important points are still involved in obscurity : Philippi 

 follows Cuvier generally in dividing the Gasteropoda into 

 the following eight orders : — 



L Pecttnibranchiata, — Organs of respiration in 

 the shape of a comb, and for the most part single ; the 

 animal forming a shell. 



2. ScuTiBRANCHiATA. — Organs of respiration comb- 

 like, but generally double. Shell snail-shaped or cup- 

 shaped. 



3. Cyclobranchiata. — Organs of respiration placed 

 in a circle round the body, in the form of little leaves. — 

 Shell spiral or cup-shaped. 



4. Cirribranchiata. — Organs of breathing hairlike, 

 situated in two lobes above the neck ; the foot like a pro- 

 boscis. Shell tubular, slightly curved, and open at both 

 ends. 



5. Tectibranchiata. — Organs of breathing unsym- 

 metrical ; more or less covered by the mantle. Shell 

 sometimes completely enclosing the animal; at others 

 rudimentary and internal. 



6. PuLMONATA. — The animals breathe air through a 

 lung cavity, or have proper gills. They live on land or in 



