346 



MOLLUSCA 

 Order I. Tetrabranchia. 



With four gills, four auricles, and four nephridia; numerous tentacles without 

 suckers, a well-developed chambered shell (fig. 352), siphon of two separate 

 epipodia, and simple eyes (fig. 350). Four living species, all belonging to Nautilus. 



FIG. 362. Octopus bairdii* (from Verrill). A hectocotylised arm on the right side. 



363. Argonauta argo, paper sailor, female (after Rymer Jones). 



The animals, which live in the Malaysian regions, are rare, but their shells are 

 abundant. In past time the tetrabranchs were very abundant; NAUTILID^, 

 with straight (Orthoceras) or coiled shells (Goniatitcs, etc.), paleozoic. They 



