XIII] CLASSIFICATION ' 325 



Sub-claSS III. EULAMELLIBRANCHIATA. 



Lamellibraiichiata in which the filaments of the ctenidium are 

 welded into a " lamella" or plate and their berit-up ends are joined 

 to the mantle. 



Ex. Unio t Anodonta. 



Class III. SOLENOGASTRES. 



Degenerate worm-like Mollusca devoid of shell and foot and 

 with a ventral ciliated groove. There is a rudimentary radula and 

 the genital organs burst into the pericardium, the kidneys serving as 

 genital ducts. 



Ex. Ckaetoderma, Neomenia. 



Class IV. SCAPHOPODA. 



Mollusca with a tubular shell and mantle and a long cylindrical 

 foot ending in three processes. A buccal mass and pleural ganglia 

 are present. The genital organ opens into the right kidney. 

 Ex. Dentalium. 



Class V. CEPHALOPODA. 



Mollusca in which the front part of the foot surrounds the head 

 and is drawn out into sucker-bearing arms whilst the hind portion 

 of the foot forms a muscular tube. The ganglia are massed together 

 and protected by a skull : there is a buccal mass with a radula and 

 two jaws. 



Sub-class I. TETRABRANCHIATA. 



Cephalopoda with four ctenidia, four kidneys, four auricles, a 

 arge external shell, no suckers and very short arms. 

 Ex. Nautilus. 



Sub-claSS II. DIBRANCHIATA. 



Cephalopoda with two ctenidia, two kidneys and two auricles. 

 Phe shell is enveloped in the mantle and the arms are long and 

 provided with suckers. 

 Order I. Decapoda. 



Dibranchiata with two long and eight short arms. 

 Ex. Ommatostrepkes, Sepia. 



Order II. Octopoda. 



Dibranchiata with eight arms of equal length. 

 Ex. Polypus (Octopus). 



