BOXELLIA. 



85 



the shell thickened internally. Paltjdina impiira, Auct. PL 

 XXV. fig. 537. 



BITOMUS. Montf. A microscopic shell, deriving this general 

 appellation, from the appearance of a double aperture. 



BIVALYE. A shell composed of two equal, or nearly equal princi- 

 pal parts, each part having a separate nucleus, turning upon each 

 other by means of a hinge. The class Conchifera of Lamarck, and 

 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 tenta- 

 cula. 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 accessory 

 valves. These are still fairly bivalve shells, although the genus 

 Pholas has been placed by some writers among the multivalves. 



BIVONIA. G-ray. Veemeitjs glomeratus. Brown. 



BOAR'S TUSK. A common name given to shells of the genua 

 Dentalium. One particular species has received a specific name 

 in accordance with a supposed resemblance, namely, Dentalium 

 Aprinum, (of a Boar.) 



BONELLIA. Desh. Nisso, Eisso, ante. A genus formed, in 

 the first instance, for the reception of Btjlikus terebellatus. 

 Lam. which Mr. Gr. B. Sowerby, in his Genera of Shells, united 

 with the genus Pyeamidella. M. Deshayes, however, in his 

 new edition of Lamarck, makes the genus Bonellia include seve- 

 ral species which I have arranged in the genus Eulima. Prom 

 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, umbiHcated. 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 through- 

 out its length ; aperture small, entire, angular at the extremities ; 



