CLASSIFICATION. 



95 



2. Cervicobranchiata. Blainville. Organs of respiration 

 situated in a large cavity above the neck, opening largely 

 forwards. 



3. SiPHoNOBRANCHiATA. Blainville. Organs of respiration 

 consisting of one or two pectiniform branchiae, contained in 

 a cavity in the anterior part of the back, and communicating 

 with the surrounding medium by a tubular canal attached 

 to the columella. 



4. AsiPHONOBRANCHiATA. Blainville and Deshayes. Organs 

 of respiration the same as in the preceding, except that 

 they are not prolonged into a tube, but have sometimes an 

 appendix or inferior lobe performing the same office. 



5. ScuTiBRANCHiATA. Blainville. Organs of respiration pro- 

 tected by a sub-spiral or simply covering shell. 



6. Inferobranchiata. Cuvier. Organs of respiration in form 

 of lamellae or folds, under the projecting border of the 

 mantle. 



7. Cirrhobranchiata. Blainville. Organs of respiration in 

 form of numerous long filaments borne by two radical lobes 

 above the neck. 



8. Monopleurobranchiata. Blainville. Organs of respira- 

 tion on one side only. 



9. NuDiBRANCHiATA. Cuvier. Organs of respiration consist- 

 ing of naked arborescent tufts arranged symmetrically on 

 the side and back. 



10. NucLEOBRANCHiATA. Blainville. Organs of respiration in 

 form of symmetrical tufts grouped with the digestive or- 

 gans into a mass or nucleus on the upper and posterior 

 part of the back. 



11. Cryptobranchiata. Deshayes. Organs of respiration 

 often not apparent. 



