BICATILLUS. Sw. A sub-genus of "Calyptrædæ," including those species, which have cup-shaped internal septa, as for example, Calyptræa extinctorium, fig. 235. BICONIA. Sw. A sub-genus of "Calyptrædæ," including those species in which the septum is partly spiral. BIFID. Divided, double. BIFRONTIA. Deshayes. Also OMALAXIS, Desh. _Fam._ Turbinacea, 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 mentioned character. The few fossil species which this genus contains (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 Calyptræa 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. BILOBATE. Having two prominent parts, as the outer lip of Rostellaria Pes-Peleeani, fig. 404. BIPARTITE. Composed of or divided into two parts; double; as the valves of Platylepas, fig. 19, each of which has a septiform division in the centre; also the area on the hinge of Spondylus. See Frontispiece. BIROSTRA. Sw. A genus composed of species of OVULUM, which have elongated extremities, as, for instance, Ovulum Volva, fig. 442. BIROSTRITES. Lam. (Double Beak.) A fossil formerly considered as a distinct bivalve shell, with conical umbones, and placed in the family of Rudistes by Lamarck, but now known to be an internal cast of Sphærulites, fig. 196. BISIPHYTES. Described by De Montfort as resembling a Nautilus, but having two distinct siphons. As no such fossil species is now known to Naturalists, it appears probable that De Montfort having a specimen of some Nautilus, with an accidental depression, took it for a second siphon. BITHINIA. Gray. A genus described as differing from PALUDINA, in having the operculum shelly, and the mouth of the shell thickened internally. PALUDINA impura, Auct. Fig. 537. BITOMUS. Montf. A microscopic shell, deriving this general appellation, from the appearance of a double aperture.