Part 17

BELEMNITES. Auct. ([Greek: Belemnon], belemnon, a dart, or arrow.) Fam. Orthocerata, Bl. and Lam.--Descr. Straight, conical, consisting of two parts; the external portion forming a thick solid sheath, with a cavity at the base to admit the internal portion or nucleus, which is mathematically conical, and is divided into chambers by smooth simple septa perforated by a lateral siphon.--Obs. These singular fossils, which are found in most secondary beds, have long attracted the attention of philosophers as well as of the ignorant, from whom they have received the various appellations of Thunder-Stones, Petrified Arrows, Petrified Fingers, Devil's Fingers, Spectre Candles, &c. The above description is framed to include the genera Hibolithes, Porodragus, Cetocis, Acamas, and Paclites of De Montfort, and Actinocamax, Stokes. Fig. 466 to 468.

BELLEROPHON. Montf. (or Bellerophus).--Descr. Convolute, symmetrical, umbilicated, with a double dorsal ridge; aperture wide, semilunar.--Obs. The fossils composing this genus resemble 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 Lamarck. 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-AURICULATED. Having two auricles placed at the sides of the umbones, as in Pecten, fig. 171. See AURICULATED.

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.

BIVALVE. A shell composed of two equal, or nearly equal principal parts, each part having a separate nucleus, turning upon each other by means of a hinge. The class Conchifera of Lamarck, Acephalophora of De Blainville severally include the whole of the bivalve shells; the latter name being derived from the fact that the animals have not distinct heads, and neither eyes nor tentacula. All bivalve shells are marine or fresh-water. They form the class Dithyra of Aristotle. It may be observed that some of the Acephalophora, the Pholades, for example, have small testaceous pieces fixed on the hinge, which are called accessary valves. These are still fairly bivalve shells, although the genus Pholas has been placed by some writers among the multivalves.

BOAR'S TUSK. A common name given to shells of the genus Dentalium. One particular species has received a specific name in accordance with a supposed resemblance, namely, Dentalium Aprinum, (of a Boar.)

BONELLIA. Desh. A genus formed, in the first instance, for the reception of Bulinus terebellatus, Lam. which Mr. G. B. Sowerby, in his Genera of Shells, united with the genus PYRAMIDELLA. M. Deshayes, however, in his new edition of Lamarck, makes the genus Bonellia include several species which I have arranged in the genus Eulima. From the remarks of M. Deshayes, tom. 8, p. 286, 287, we are led to suppose that the estimated difference between Eulima and Bonellia consists in the latter having the axis perforated; or in other words, umbilicated. After remarking "que Mr. Sowerby, junr. confond deux choses bien distinctes, sous le nomme d'Eulima," M. Deshayes gives the following description of his genus, (translated) "shell turriculated, smooth, polished, with the apex acute and laterally inclined; axis perforated throughout its length; aperture small, entire, angular at the extremities; columella simple and without folds; outer lip thin, simple, nearly parallel with the longitudinal axis." That author further remarks, "Mr. Sowerby, junr. à signalé cinque espèces vivant, que nous rapportons à notre genre." (Sowerby, junr. Conchological Illustrations, parts 52 and 53; 50, Great Russell Street, Bloomsbury.) The species thus selected are E. splendidula, E. marmorata, E. interrupta, E. imbricata, E. brunnea; the two last of which have the umbilicus so inconsiderable, as to be scarcely distinguishable from other species, which M. Deshayes has left in the genus Eulima, and which have a slight hollow, almost approaching to a perforation, behind the columella. Eulima marmorata, (Bonellia, Desh.) is figured in the plates, fig. 348.

BODY WHORL. The last whorl, constituting the bulk of the shell.

BORELIS. Montf. MELONIA, Bl. A genus of microscopic Foraminifera.

BORER or PIERCER. A term applied to those species of Acephalopodous Mollusca, which bore holes as dwellings in the rocks, as the Pholades, and some others.

BRACHIOPODA. Lam. A family of symmetrical bivalves belonging to the third section of Lamarck's order "Conchifera Monomyaria," described as bivalve (generally symmetrical) adhering to marine bodies, by a tendon passing through the shell, having no true ligament. What most distinguishes this family and renders it remarkable is the structure of the animal. It has two elongated, tendril-shaped arms. When the animal is in a state of repose these arms are coiled up spirally and enclosed in the shell, but when required for use, are unfolded and extended. This family contains the genera Orbicula, Terebratula and Lingula, in the system of Lamarck, to which may be added Thecidium, Productus, Spirifer, Magas, Pentamerus, Crania, Strigocephalus, Strophomena, and some others enumerated in the explanation of figures 201 to 219. The above genera may be thus distinguished.

1. ORBICULA. Umbones central; byssus passing through a hole in the flat valve. Fig. 201.

2. ATRYPA. Without foramen or space between the valves. Fig. 203.