72 CLASSIFICATION. 



SYSTEMATIC. 



CLASS GASTEROPODA. 



Head distinct, furnished with eyes and tentacles. Body usually 

 protected by a spiral or conical univalve shell. Lower surface 

 of body developing a thickened, expanded, creeping disk or 

 foot. 



ORDER I. PROSOBRANCHIATA. 



Animal, creeping or swimming, protected by a shell usually 

 large enough to contain it. Breathing organs (branchiae), plume- 

 like, situated in advance of the heart. Sexes distinct. 



(Section A. SIPHONOSTOMATA.) Animal with its mantle margin 

 prolonged into a siphon conveying the water into the branchial 

 chamber. Carnivorous. Marine. The shell is spiral, the axis 

 usually imperforate, the aperture prolonged into a canal, or 

 simply notched below. Operculum lamellar, horny. 



(Section B. HOLOSTOMATA.) Respiratory siphon wanting, or 

 represented by a mere lobe in the collar of the mantle. Shell 

 spiral or limpet-shaped, generally globular or pyramidal, with 

 the aperture entire below, and rounded. Marine, fluviatile or 

 terrestrial. Phytophagous usually. (Natica is carnivorous.) 

 Operculum spiral, horny or calcareous. 



SIPHONOSTOMATA. 



Family MURICID^E. Shell spiral, fusiform ; aperture more or 



less canaliculate, or simply notched in front. 

 Sub-family Muricinae. Shell canaliculate ; whorls crossed by 



varices. Operculum ovate. Nucleus subapical. 

 Sub-family Purpurinse. Shell with very short canal, or simply 



notched in front ; but frequently ribbed or nodulous ; colu- 



mella usually broad and flattened ; operculum oblong, nucleus 



elongate, forming the long outer edge. 



The above division into two sub-families holds good as to a 

 majority of the species, but does not cover them all. Thus, 



