GASTEROPODA. 201 



trally 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 con- 

 spicuous eyes behind them ; ventral fin flattened, fan-shaped, furnished with a 

 small fringed sucker ; tail pointed, operculigerous. 



Distr. 15 sp. Warmer parts of the Atlautic, Canary Ids. 



Sub-genus. Oxygyrus, Benson. Syn. Ladas, Cantraine ; Helieo-phlegma, 

 D'Orb. 0. Keraudrenii, PL XIII. figs. 24, 25. Shell milky, narrowly um- 

 bilicated on both sides ; nucleus not visible ; back rounded, keeled only near 

 the aperture; body whirl, near the aperture, and keel cartilaginous; no aper- 

 tural slit ; operculum trigonal, lamellar." 2 sp. Atlantic. Medit. 



The Atlanta was discovered by Lamanon, who supposed it to be the 

 living analogue of the Ammonite. The operculum of Oxygyrus (PI. XIII. 

 fig. 25) is singularly like the Trigonellites (p. 80) ; that of Atlanta (fig. 22) 

 is the only example of a dextral operculum to a dextral shell (p. 102). 



PORCELLIA, Leveille. 

 Ex. P. Puzosi, PI. XIV. fig. 29. 



Shell discoidal, many whirled ; whirls keeled or coronated ; nucleus spiral ; 

 aperture with a narrow dorsal slit. 



Fossil, 10 sp. Devonian Trias. Brit. Belgium. 



BELLEROPHON, Monfort. 



Ex. B. bi-carinatus, Lev. PL XIV. fig. 27. Syn. Euphemus, M'Coy. 



Shell symmetrically convoluted, globular, or discoidal, strong, few- 

 whirled; whirls often sculptured; dorsally keeled; aperture sinuated and 

 deeply notched on the dorsal side. 



Fossil, 70 sp. L. Silurian Garb. N. America, Europe, Australia. 

 The name Bucania was given by Hall to the species with exposed whirls ; 

 in B. expansus, PL XIV. fig. 28, the aperture of the adult shell is much ex- 

 panded, and the dorsal slit filled up. (Salter.} 



JBellerophina, D'Orb (not Forbes) is founded on the Nautilus minutus. 

 Shy. PL XIV. fig. 26, a small globular shell, spirally striated, and devoid 

 of septa. It is found in the gault of England and Trance. 



CYRTOLITES, Conrad. 



type, C. ornatus, PL XIV. fig. 30. 



Etym. Kurtos, curved, lithos, stone. 



Shell thin, symmetrical, horn-shaped or discoidal, with whirls more or 

 less separate, keeled and sculptured. 



Fossil, 13 sp. L. Silurian Garb, N. America, Europe. 



? Ecculiomphalus (Bucklandi) Portlock, PL XIV. fig. 31. L. Silurian, 

 Brit. U. States. Shell thin, curved, or discoidal with few widely separate 

 whirls, slightly unsymmetrical, keeled. 



