5-16 



MOLLUSCA 



Order I. Tetrabranchia. 



With four sills, four auricles, and four ncphridia; numerous tentacles without 

 suckers, a weli-developed chambered shell (hi^. J5^), siphon of two s_eparate 

 epipodia, and simple eyes i,tig. ss°}- ^''-'•^^ iiymg species, all belonging to Xaiilihis. 



Fig. ^02. — Oclopiis bairdii* (.from ^>^rill). A hcctocotylised arm on the right side. 







Fig. 363. — Argonaiila 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 aliundant; N.M'Tilip.t., 

 with straight {Orlhoccras) or coiled shells (Gonialilcs, etc.), paleozoic. They 



