258- CLASSIFICATION. 



Troschel's first section commences with the Pulmonates, but 

 Morch considers very doubtful their having a true pulmonary 

 sack closed by a contractile opening. Gray calls these respira- 

 tory organs of the Cyclostomaa " gills vascular, branched," and 

 " gills indistinct in the form of series of vessels on the inner 

 surface of the mantle." 



" Sect. 1. Fam. 1, Aciculacea ; 2. Pomatiacea ; 3. Cj'-clotacea ; 

 4. Cyclostomacea. 



Sect. 2. Respiring by branchiae and lungs ; Ampullariacea. 



Sect. 3. Branchiferous Holostomata. Fam, 1. Valvatse ; 2. 

 Hydrobise (Lithoglyphus) ; 3. LittorinidiB ; 4. Rissoidse ; 5. 

 Paludinidse ; 6. Melaniidse ; 7. Potamidse ; 8. Cerithiidee (Plan- 

 axis). 



The Aporrhaidai form a passage between the Cerithiidas and 

 Strombidse. Crepidula and Capulus belong with Hipponyx in a 

 group, notwithstanding differences in the labial palpi. Omistidae 

 connects the Crepidulidse with the Heteropods. 



Ovulidae (including Pedicularia), generally placed close to 

 C^^prsea, is strongly distinguished from the latter by its non- 

 retractile proboscis. Notwithstanding this character, Morch 

 considers it intermediate between Cassis and Cyprasa. 



The 3d section of Troschel (trunk retractile from the base) 

 contains the genera which Morch united in 1852 in the family 

 Tritonidae, namely : Cassis, Dolium, Pyrula, Triton, Ranella. 



Onchidiopsis, Velutina, Marsenia, Tylodina, form, probably, a 

 very natural division, notwithstanding the want of the two 

 lateral teeth in Marsenia. The family Naticidse stands next in 

 relationship. It is in the Tteniogiossata that the greatest 

 incertitude relative to a natural grouping of the families exists; 

 in the orders which follow, these relationships are more positively 

 defined. 



Order 2. Rhachiglossata, Troschel. Never more than three 

 rows of teeth. All mollusks having coriaceous ovisacs, hereto- 

 fore known, belong to this order. 



Sect. 1. Marginella, Voluta, Volutilithes, connecting with 

 Cryptochorda and Harpa ; Oliva, Ancillaria, Bullia,Nassa, Mitra, 

 Columbella. 



Sect. 2. Buccinum, Fusus, Fasciolaria, Turbinella, Purpura, 

 Murex, Magilus. 



Order 3. Toxoglossata. Two rows of teeth. Stimpson has 

 recently discovered a median tooth in Clionella sinuata, Born. 

 Conus, (Borsonia?), Pleurotoma, Clionella, Terebra, Cancellaria, 

 Halia, Lachesis? 



Supra-class II. Agama, Latr. (Diotocardia, Morch). 

 Mollusks witho^^t copulative organ. Heart with two auricles, 

 placed nearlj' always aroUnd the intestine. 



