82 BTLABIATED. 



symmetrical, umbilicated, with a double dorsal ridge ; aperture 

 wide, semilunar. — Obs. The fossils composing this genus re- 

 semble Nautilus in general appearance, but not being chambered 

 shells they approach very near to Argonauta, from which they 

 differ only in the thickness of their shell and in roundness of 

 their external form. This genus is erroneously placed by De 

 Montfort among chambered shells, and by De Blainville next to 

 Bulla. It belongs to the Monothalamous Cephalopoda of La- 

 marck. This fossil is found principally in the Carboniferous 

 Limestone. Fig. 486, 487, represent B. tenuifasciata. 



BELOPTERA. The bony support of a species of Cuttlefish, partly 

 resembling Sepia. 



BIAPHOLIUS. Leach. A genus believed to be identical with Hiatella. 



BI-AUBICULATED. Having two auricles placed at the sides of 

 the umbones, as in Pecten, fig. 171. See Aurictjlated. 



BICATILLUS. Sw. A sub-genus of " CalyptrsBdae," including 

 those species, which have cup -shaped internal septa, as for ex- 

 ample, Calyptrsea extinctorium, fig. 235. 



BTCONIA. Sw. A sub-genus of " Calyptrsedse," including those 

 species in which the septum is partly spiral. 



BIFID. Divided, double. 



BIFRONTIA. Deshayes. Also Omalaxis, Desh. Fam. Turbina- 

 cea, Lam. — Descr. Discoidal, planorbicular, with whorls sometimes 

 not contiguous ; umbilicus deep, keeled at the margin ; aperture 

 subtriangular, somewhat dilated ; outer lip acute, separated by a 

 deep notch at both extremities. — Obs. We do not see any reason 

 for separating this genus from Solarium, except the last men- 

 tioned character. The few fossil species which this genus con- 

 tains (Solarium disjunctum, Bifrons, &c.) are found principally 

 in the Paris basin. Fig. 354. Solarium Bifrons. 



BI -FURCATE. Double pronged, or having two points. Ex, the 

 internal appendage of Calyptrsea Equestris, fig. 234. 



BIGENERINA. D'Orb. A genus of microscopic Foraminifera. 



BILABIATED. Having the edge of the outer lip as it were 

 doubled, by one part of the lip being more thickened and reflected 

 than the other, so as to form a ledge, or second lip. 



