Organs employed in the Classification of the Mollusca. 395 



Tectibranchia : Pyramidella, Obeliscus, Odostomia, Chemnitzia, 

 Actceon, Bulla, Aplysia, Notarchus. 



Pteropoda : Gymnosomata, — Clione, Pneumodermon {Ianthinal) ; 

 Thecosomata, — Clio, Hyalcea, &c. 



Gymnobranchia. 



1. Pygobranchia : Doridce, &c. 



2. Pleurognatha : Pleurophyllidia,Dendronotus, Tritonia, Bornella, 

 jEolis, Glaucus, &c. 



3. Pellibranchia : Tethys, Chionera, Hermcea, Elysia, Limapontia, 

 Pelta, &c. 



Class II. EXOPHALLIA (Arthroglossata olirn). 



Sexes distinct ; male organ not retractile (often concealed in the bran- 

 chial cavity or in the tentacle). Mouth predominantly suctorial. 

 Lingual strap not having more than seven rows of teeth. 



T^niog loss ata. Tongue with seven rows of teeth, with reflected 

 edge. Larva of the marine species swimming. 



A. Rostrifera. With a short muzzle, not retractile. 

 a., terrestria. Cyclostomacea (Truncatella). 



ft. fluviatilia. Ampullaria,-Paludina, Melania, Potamides, Ceri- 

 thium, Turritella (with nine? rows of teeth), Littorina, Lacuna, 

 Velutina, Onchidiopsis . 



y. parasitica. The eggs hatched in pouches attached to the in- 

 side of the shell. Vermetus, Crepidula, Hipponyx, Capulus. 



8. Pelagica Heteropoda. Firoloides, Pterotrachc?a, Cardiapoda, 

 Peltaria*, Carinaria, Helicophlegma, Atlanta, Bellerophon, 

 Onustus. 



e. Strombi. 



B. Proboscidifera. Rostrum retractile. Natica, Ovula, Pedicularia, 



Trivia, Cyprcea, Cussis, Dolium, Pyrula, Triton, Trichotropis, 

 Aporrhais. 



Rhachiglossata. Tongue not having more than three rows of 

 teeth, which are not reflected at the edge. Rostrum long, retrac- 

 tile (without cheek-plates?). Eggs deposited in cartilaginous cap- 

 sules, which the young leave when the metamorphosis is complete. 

 Maryinella, Voluta (lateral teeth absent), Harpa, Oliva, Ancillaria, 

 Bullia, Nassa, Buccinum, Fusus, Fasciolaria, Turbinella, Murex, 

 Purpura {Magilusl), Mitra. 



Toxoglossata. Mouth with a suctorial veil. Tongue (?) with 

 subulate teeth provided with an internal or external veniferous 

 canal. Conns (Borsonial), Pleurotoma, Clionella, making a transi- 

 tion to Terebra, Cancellaria. The egg-cases of this division are 

 probably like the preceding ; but direct observation is wanting. 



Series II. DIOTOCARDIA. 



Heart with two auricles. (That this character has no relation to the posi- 

 tion of the gills, as Prof. Huxley suggested, is evident in the case of 

 Pleurophyllidia, which, according to Messrs. Hancock and Bergh, have 



* Carinaria depressa, Rang, Man. t. 3. f. 1 . 



