344 MAIs^UAL OF THE MOLLUSCA, 



can retire ; gills contained in a dorsal mantle cayity : lingual 

 teeth, similar to Carinaria. 



Shell symmetrical, discoidal, sometimes closed by an opor- 

 cnlum. 



Atlanta, Lesueui-. 



Type, A. Peronii, PI. XIY., Figs. 21-23. 



Synonym, steira, Esch. 



Shell minute, glassy, comj^ressed and prominently keeled; 

 nucleus dextrally spiral; aperture narrow, deeply notched at 

 the keel; operculum ovate, pointed, lamellar, with a minute, 

 apical, dextrally spiral nucleus. 



Animal 3-lobed ; head large, sub -cylindrical ; tentacles 

 conical, with conspicuous eyes behind them ; yentral fin 

 flattened, fan- shaped, furnished with a small fringed sucker; 

 tail pointed, operculigcrous. 



Distribution, 18 species. "Warmer parts of the Atlantic, 

 Canary Islands. 



Sub-genus. Oxygyrus, Benson. Synonyms, Ladas, Cantraine ; 

 Helico-phlegma, D'Orbigny. O. Keraudrenii, PI. XIII., Pigs. 

 24, 25. Shell milky, narrowly umbilicated on both, sides ; 

 .nucleus not visible ; back rounded, keeled only near the aper- 

 ture ; body whorl, near the aperture, and keel cartilaginous ; 

 no apertural slit; operculum trigonal, lamellar. 4 species. 

 Atlantic, Mediterranean. 



The Atlanta was discovered by Lamanon, who supposed it to 

 be the living analogue of the Ammonite. The operculum of 

 Oxygyrus (PI. XIII., Pig. 25) is singularly like the Trigonellites 

 (p. 182) ; that of Atlanta (Fig. 22) is the only example of a 

 dextral operculum to a dextral shell (p. 207). 



PoECELLiA, Leveille. 



Example, P. Puzosi, PL XIY., Fig. 29. 



Shell discoidal, many-whorled ; whorls keeled or coronated ; 

 nucleus spiral ; aperture with a narrow dorsal slit. 



Fossil, 10 species. Upper Silurian — Trias. Britain, Bel- 

 gium. 



Bellerophon, Montfort. 



Example, B. bi-carinatus. Ley. PI. XIY., Fig. *27. 



Synonym, Eupbemus, M'Coy. 



Shell symmetrically convoluted, globular, or discoidal, strong, 

 few-wh.orled ; whorls often sculptured ; dorsally keeled ; aper- 

 ture sinuated and deeply notched on the dorsal side. 



