BASE. In all shells which are attached to sub-marine substances, the base is that part of the shell which forms the point of attachment,--as for instance, the attached valve of Spondylus, the basal plate of Balanus, the lower part of the peduncle of Pentelasmis; in Unattached Bivalves, the margin opposite to the umbones, where the foot of the animal, or the part analogous to it, protrudes; in spiral univalves, the aperture, which rests on the back of the animal when walking. Lamarck and some other authors have used the term _base_ as simply opposed to apex, and apply it to the anterior of the aperture. BATOLITES. Montf. HIPPURITES, Auct. BEAK. The Apices, or points of the valves of a bivalve shell, generally termed UMBONES, in descriptions. Also any part which is rostrated or drawn out like a beak. BEAKED. See BEAK and ROSTRATED. BEAR'S-PAW-CLAM. The common name for Hippopus maculatus, a representation of which is given in the plates, fig. 156. 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.