AZYGOBRANCHIA.] M L L U S C A 649 TABULAR VIEW OF THE SUBDIVISIONS OF THE CLASS GASTROPODA, ARRANGED so AS TO SHOW THEIR SUPPOSED GENETIC RELATIONSHIPS. Class. GASTROPODA. (Archisopleurum. ) Sub-class 1. ISOPLEURA. 3 > Sub-class 2. ANISOPLEURA. (Archicuthyiicurum. ) Branch a. STREPTONEURA. ( Archizygobranchium. ) Branch b. EUTHYNEURA. (Archiopisthobranchium. ) O p Order 1. ZYGOBRANCHIA. Order 2. AZYGOBRANCHIA. (Archiholochlamydum. ) Sect. a. ReptarUia. Sect. b. Natantia. Order 1. OPISTHOBRANCHIA. (Archipalliatum. ) I Order 2. rULMONATA. (Archibasommatum. ) Sect. a. Palliata. Sect. b. Non-Palliata. w tc H-" . ? 38 as - S i J? & 1-1 Family 11. Naticidss. Genera : Natica, Lam. ; Sigarctus, Lam. ; Xeritopsis, Gratel. Family 12. Entoconchidse. The single genus and species EntoconcJut mirabilis, discovered by Joh. Miiller in 1851, parasitic in Synapta digitata. The adult form is not known. Family 13. Marsenidte. Genera : Marscnia, Leach ; Onchidiopsis, Beck. Family 14. Acm&idae. Genera : Acmaea, Eschsch. ; Lottia, Gr. ; (probably these will be found to belong to the Zygobranchia). Family . Capulida. Genera : Capulus, Montf. ; Calyptrsea, Lam. (fig. 40) ; Trochita, Schum. Family 1 6. Littorinidss. Genera : Littorina (the Periwinkles, fig. 46) ; Modulus, Gray ; Lacuna, Turt. ; Rissoa, Frem. : Hydrobia, Hartm. ; Assiminia, Leach. Family 17. Paludinidse. Genera : Paludina (River-Snail) (figs. 7, 21) ; Bithynia, Gray ; Tanalia, Gray. Family 18. Valvatidte. Genus : Valvata (fig. 45), fresh-water. Family 19. Ampullaridae. Genus : Ampullaria (can breathe air by means of the walls of the pallial chamber as well as water by the gill ; fresh-waters of tropical America, Africa, and East Indies). Sub-order 2. Pncumonochlamyda. Characters. Pallial chamber a lung-sac; no gill; mouth on a rostrum, not a retractile proboscis ; terrestrial habit. Family 20. Cydostomidae. Genera : Cyclostoma, Lam. ; Cyclojyhorus, Montf. ; Ferussina, Gratel. ; Pupina, Vignard. Family 21. Helicinidae (radula rhipidoglossate rather than tcenio- glossate). Genera : Stoostoma, Adams ; TrocJiatclla, Swains. ; Hclicina, Lam. ; Proserpina, Guild. Family 2 2. Aciculidae. Genera : Acicula, Hartin. ; Gcomclania, Pfr. Sub-order B. Siphon ochlamy da. CJMractcrs. Reptant Azygobranchia with the margin of the mantle drawn out to form a trough-like siphon which notches the lip of the shell ; shell always spiral ; usually an operculum, horny or lamelliform ; either a rostrum or a retractile proboscis ; exclusively marine ; mostly carnivorous.
- Tsenioglossa (3.1.3).
Family 1. Slr&mbidas. Genera : Strombus, L. ; Pteroceros, Lam. ; Eostcllaria, Lam. (fig. 43). Family 2. Aporrhaidas. Genus : Aporrhais, Da Costa. Family 3. Pedicular idas. Genus : Pedicularia, Swains. Family 4. Dolidse. Genera: Cassis, Lam.; Cassidaria, Lam.; Dolium, Lam.; Flcula, Swains. Family 5. Tritonidse. Genera : Tritonium, Cuv. (fig. 42) ; Ranella, Lam. Family 6. Cypraeidae (the Cowries). Genera : Cypraea, L. ; Ovulum, Brug. (fig. 41) ; Erato, Risso.
- Toxiglossa (1.0.1).
Family 7. Conidae. Genus : Comis, L. Family 8. Tcrcbridas. Genus : Tcrcbra, Adans. Family 9. Pleurotomidas. Genus : Plciirotoma, Lam. Family 10. Canccllaridse. Genus : Cancellaria, Lam.
- Rachiglossa (1.1.1 or .1.).
Family 11. Muricidee. Genera : Murex, L. ; Trophon, Montf. ; Fusus, Brug. ; Pyrula, Lam. (fig. 38) ; Turbinella, Lam. Family 12. Buccinidte. Genera : Buccinum, L. ; Nassa, Lam. (fig. 5) ; Pnrpura, Brug. (fig. 47); Concholcpas, Lam.; Magilus, Montf. Family 13. Mitridae. Genus : Mitra, Lam.
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