Guide to the Invertelrata. 



Collusca. or Odontophoea, the mouth being furnished with a tonj^ue, 



ALLEBIES pi'ovided with appropriate muscles, known as the lingual ribbon 



or odontophore, the surface of which is covered by a chitinous 



membrane beset with minute teeth forming a flexible rasp, or 

 radula. This division includes the Cephalopoda, Scaphopoda, 

 Amphineura, and Gasteropoda. The various members of this 



^^a^ 



Fio. 10.— Part of the radula of Auricula, with central {c) and lateral {T) teeth 

 and (u) uncini more enlarged. 



division generally lead an active and sometimes aggressive 

 existence. 



The second division, named Acephala (or Lipocephala), includes 



Fig. 11.— Part of the radula of Siphonaria, sp., from the Cape, c, central 



only the Lamellibranchiata. In these the head is aborted; no 

 cephalic eyes are present; and the mouth is destitute of biting, 



