146 DOLIUM. 



DISCODOMA. Sw. A sub-genua of LueemiiMD, Sw. (Helix), thus 

 described, " teeth none ; aperture angulated ; the inner lip nearly- 

 obsolete ; the outer only slightly thickened ; margin carinated." 



DISCOID AL. (Discus, a circular plane.) A spiral shell is said 

 to be discoidal, when the whorls are so horizontally convolute as 

 to form a flattened spire. £x. Planorbis, fig. 311. Orbidites 

 Discus, fig, 479. 



DISCOLITES. Montf. A genus of microscopic Eoraminifera. 



DISCONTINUOUS. Interrupted. Ex. The siphon of Nautilus 

 is discontinuous, i. e. its termination in one chamber does not 

 reach to its commencement in the next. The varices of Triton, 

 occurring in difierent parts of the whorls, do not form the con- 

 tinuous ridges which characterize the generality of the Hanellse. 



DISCOEBITES. Lam. A genus of microscopic Foraminifera, ^' 



DISTANT. The teeth on the hinge of a bivalve shell are said to 

 be distant when they are said to be remote from the umbones. 



DIYAEICATED. Diverging, meeting in a point, as the teeth on 

 the hinge of Placuna, fig. 184. T^^ 



DOLABELLA. Lamarck. (Dim. from Dolahra, a hatchet.) 

 Fam. Aplysiacea, Lam. and Bl. — Descr. Hatchet-shaped, arched, 

 covered with a horny epidermis ; posteriorly attenuated, thick- 

 ened, sub-spiral, anteriorly plane, broad, thin; posterior margin 

 reflected. — 06s. The two or three species of DolabeUa known are 

 inhabitants of the Indian Ocean. They were placed by Linnaeus 

 in his very convenient genus BuUa, under the name of B. dubia. 

 PL xiii. fig. 255, Dolabella Eumphii. 



DOLIUM. Brown, (1756.) (a fun.) Fam. Purpurifera, Lam. 

 Entomostomata, Bl. — Descr. Thin, ventricose, oval, or globular, 

 with a short spire; large aperture terminating in a reflected canal, 

 and spirally ribbed or grooved external surface ; outer lip ere- 

 nated ; inner lip reflected over part of the body whorl, which 

 terminates in a tumid varix ; epidermis light, homy. Mediter- 

 ranean and East Indian. — Obs. This genus is distinguished from 

 Cassis by the outer Hp, which is not reflected. The species which 

 are not so round as the others, as D. Perdix, Auct. have been 

 separated under the name Perdix, as if generically distinct. 



