CLASSIFICATION. 95 
2. Cehvicobranchiata. 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. 
