BULLA. Auct. _Fam._ "Bulléens," Lam. Akera, Bl.--_Descr._ Generally thin, smooth, oval, oblong or cylindrical, more or less convolute; spire short, depressed, or hidden by the last whorl; aperture long, wide in front, gradually narrowing towards the spire; outer lip thin; inner lip spread over a part of the last whorl.--_Obs._ The shells composing this genus are very variable in form. The light horny species with an elastic lip is called Akera, fig. 247. The more decidedly convolute species with hidden spires are the Atys, Montf. B. Naucum, fig. 250. B. Lignaria, fig. 251, is Scaphander of Leach. The light, thin species, with extremely wide aperture, fig. 248, is Bullæa aperta, Lam. The genus Bullinula of Dr. Beck, consists of those species which have more produced spines, fig. 253. The Bullæ are marine, and inhabit all climates. The fossil species occur in tertiary beds. BULLÆA. Lam. BULLA aperta, Auct. fig. 248. BULLÆANA. ("Bulléens, Lam.") A family belonging to the first section of Lamarck's order, Gasteropoda, containing the genus Bulla. The genera Bullæa, Akera, Aplustra, Atys, Scaphander, Bullinula, into which it has been divided, may all be fairly included under the name BULLA. BULLIA. Gray. A genus of shells partly resembling Buccinum, and Terebra in general form, being more elongated than the former and more ventricose than the latter. Mr. Gray remarks in the Synopsis of the British Museum, page 114, that the Bulliæ resemble the Nassæ in most characters, "but they have a very large, broad foot, and the hinder part of the inner lip of the shell being extended beyond the mouth, forms a raised enamelled band round the suture of the whorls, as is also the case with the Ancillariæ and some Volutes." Bullia vittata, fig. 427, is an example of the genus. The name Subula is given by De Blainville to the other species of Terebra, so that if both these genera were admitted, the old genus Terebra must be expunged. BULLINULA. Beck. Species of BULLA, with produced conical spires, fig. 253. BYSSOARCA. Sw. (_Byssus_ and _Arca_.) _Fam._ Arcacea, Lam. A genus of bivalve shells, composed of the Arca _Noæ_, and several other species, separated from the genus Arca on account of their shells being attached by means of a byssus passing through an hiatus in the ventral margins. B. _Noæ_, fig. 132. The species occur in Southern Europe, East and West Indies, China; also, on the coasts of Great Britain. BYSSOMYA. Cuvier. (_Byssus_ and _Mya_.) De Blainville states that although the shell of this proposed genus resembles Saxicava, the animal is sufficiently different to justify the separation.