40 EBURNA. 
ened, sub-spiral, anteriorly plane, broad, thin; posterior mar- 
gin reflected. Obs. The two or three species of Dolabella 
known are inhabitants of the Indian ocean. They were placed 
by Linneus inhisvery convenient genus Bulla, under the name 
B. dubia. Fig. 255, Dolabella Rumphii. 
DO'LIUM. Lam. (Atun.) Fam. Purpurifera, Lam. Ento- 
mostomata, Bl. Descr. Thin, ventricose, oval or globular, with 
ashort spire, large aperture terminating in a reflected canal, and 
spirally ribbed or grooved external surface; outer lip crenated; 
inner lip reflected over part of the body whorl, which terminates 
in a tumid varix; epidermis light, horny. Obs. This genus is 
distinguished from Cassis, by the outer lip, which is not reflected. 
The species which are not so rotund as the others, Hw. D.Perdix, 
Auct. have been separated under the name Psrpix, as generic. 
Fig. 420. Dolium Maculatum. 
DONAX. Linn. (A wedge.) Fam. Nymphacea, Lam. Con- 
chacea, Bl. Descr. Equivalve, inequilateral, trigonal, with the 
anterior side short, straight, plane ; the posterior side elongated, 
drawn toa narrow, rounded termination; hinge with two cardi- 
nal teeth in one valve, one in the other, and one or two, more or 
less remote, lateral teeth; ligament external; muscular impres- 
sions two in each valve; palleal impression sinuated posteriorly. 
Obs. The Capsz have not the crenated margins, the short an- 
terior side, and the distinct lateral teeth, which characterize the 
Donaces. Some species of Erycina resemble Donax in general 
form, but are at once distinguished by the ligamentary pit in the 
hinge. Fig. 108, D. cuneatus. 
DORSAL Shell. Is one placed upon the back of the animal. 
The dorsal part of a bivalve shell is that on which the hinge is 
placed, the opposite margins are termed ventral. The dorsal 
surface of a spiral univalve, is that which is seen when the aper- 
ture is turned from the observer. The dorsal valve is the up- 
permost in Brachiopodous bivalves. 
DORSA’LIA. Lam. (Dorsum, the back.) The first family of 
the order Annelides Sedentaria, Lam. containing Gen. Aren- 
icola, not a shell; and Siliquaria, fig. 1. 
DOSI'NA. Schum. Venus Verrucosa, Cassina, and similar species. 
Fig. 119, a. 
DREISSINA. Myvritus Polymorphus, Auct. Fig. 159. 
EBURNA. Lam. (£burnus, ivory.) Fam. Purpurifera, Lam. 
Entomostomata, Bl. Deser. Oval, thick, smooth, turrited, um- 
bilicated; spire angulated, acute, nearly as long as the aperture ; 
aperture oval, terminating anteriorly in a canal, posteriorly ina 
groove; outer lip slightly thickened with an anterior notch, 
which terminates a spiral fold surrounding the body whorl; 
umbilicus generally covered by the thickened columellar lip. 
Obs. The beautiful shells called Ivory Shells, which originally 
constituted part of this genus, are now placed in the genus 
