Part 33

DOLIUM. D'Argenville. (a tun.) 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 crenated; inner lip reflected over part of the body whorl, which terminates in a tumid varix; epidermis light, horny. Mediterranean and East Indian.--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, as D. Perdix, Auct. have been separated under the name Perdix, as generic. Fig. 420, Dolium Maculatum.

DONAX. Auct. Fam. Nymphacea, Lam. Conchacea, Bl.--Descr. Equivalve, inequilateral, trigonal, with the anterior side short, straight, plane; the posterior side elongated, drawn to a narrow, rounded termination; hinge with two cardinal teeth in one valve, one in the other, and one or two, more or less remote lateral teeth; ligament external; muscular impressions two in each valve; palleal impression sinuated posteriorly.--Obs. The Capsæ have not the crenated margins, the short anterior 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. Sandy shores in all climates. Fig. 108, D. cuneatus.

DORSAL. A dorsal shell is one placed upon the back of the animal. The dorsal margin 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 aperture is turned from the observer. The dorsal valve is the uppermost in Brachiopodous bivalves. The dorsal part of a symmetrical convolute univalve, such as the Nautilus and Ammonite is that part of the whorls which is at the greatest distance from the spire, that is, the outer part of the whorls. Thus the situation of the siphon is said to be dorsal when it pierces the septum near the outer edge of the whorls. The dorsal part of symmetrical conical univalves, such as Patella, is the upper part, on which the apex is placed.

DORSALIA. Lam. (Dorsum, the back.) The first family of the order Annelides Sedentaria, Lam. containing the genera Arenicola, not a shell, and Siliquaria, fig. 1, which is now considered as a true mollusc, and placed next to Vermetus.

DOSINA. Schum. VENUS Verrucosa, Casina, and similar species. Fig. 119, a.

DREISSINA. MYTILUS Polymorphus. Auct. fig. 159. This genus differs from Mytilus principally in the characters of the animal. The shell is characterized by a small septiform plate under the hinge within. Fluviatile, Europe and Africa.

EBURNA. Lam. (Eburneus, ivory.) Fam. Purpurifera, Lam. Entomostomata, Bl.--Descr. Oval, thick, smooth, turrited, umbilicated; spire angulated, acute, nearly as long as the aperture; aperture oval, terminating anteriorly in a canal, posteriorly in a groove; outer lip slightly thickened with an anterior notch, which terminates in 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 Ancillaria by authors. They differ from the present genus Eburna, in having the sutures of the spire covered with a polished enamel. (A. glabrata, fig. 455.) The Eburnæ resemble in some respects the genus Buccinum, but a glance at the figure will enable the reader to distinguish a true Eburna from all other shells. Fig. 426 is Eburna Zeylanica. A catalogue of 9 species is given in part 20 of the Conchological Illustrations published by the Author, accompanied by figures of several species.

ECHIDNIS. Montf. Described as a straight, chambered, annulated, fossil shell, computed from the extremely gradual increase in diameter of the fragments to be at least sixteen feet long. Found in marble from the Pyrenees.

ECHINELLA. Sw. A sub-genus of Monodonta. Sw. Malac. page 352.

EFFUSE. (effundo, to pour out.) The aperture of an univalve shell is said to be effuse when there is a notch in the margin which would suffer a liquid to escape, and thus prevent it being filled to the brim.

EGEON. Montf. A genus of microscopic Foraminifera.

EGERIA. Lea. (Contrib. to Geol. p. 49, pl. 1.) A genus of fossil bivalves, described as very variable in form, with or without lateral teeth, sometimes a crenated margin, &c. The only certain characters appear to be that they have two diverging cardinal teeth in each valve, one of which is bifid; and an external ligament. Lea states that the Egeriæ should be placed between the Sanguinolariæ and the Psammobiæ, which two latter genera have been united by Sowerby. Fig. 103, E. Triangulata, from the tertiary formation of Alabama.

ELENCHUS. Humph. A genus composed of TROCHUS Iris, Auct. and other similarly formed species. It is the same as CANTHARIDUS of Montfort.

ELEPHANT'S TUSK. The common name given by dealers to shells of the genus Dentalium. Ex. D. octogonum, fig. 2.

ELEVATED. A term which is applied by some conchological writers to the spire of an univalve shell when it consists of numerous whorls drawn out into a telescopic form. Other authors use the term elongated, or the more simple one 'long,' to express the degree of elevation.

ELISMA. Leach. A sub-genus of Bulinus. B. acutus, Auct. Gray, Turton, p. 185.

ELLIPSOLITHES. Montf. ([Greek: Elleipsis], ellipsis, oval; [Greek: lithos,] lithos, stone.) A genus composed of Ammonites, which instead of being regularly orbicular, take an elliptical or oval form. This character appears to be accidental, as some individuals of the same species, both of Nautilus and Ammonites, are round, while others are compressed into an oval form.

ELLIPSOSTOMATA. Bl. ([Greek: Elleipsis], ellipsis, oval; [Greek: stôma], mouth.) The third family of the class Asiphonibranchiata, Bl. The shells of this family are described as of various forms, generally smooth; the aperture longitudinally or transversely oval, completely closed by a horny or shelly operculum. This family contains the genera Rissoa, Phasianella, Ampullaria, Helicina, and Pleuroceras.

ELLIPTICAL. ([Greek: Elleipsis], ellipsis.) Oval. Applied to any shell or part of a shell, having that form.

ELMINEUS. Leach. Order, Sessile Cirripedes, Lam.--Descr. Four unequal valves, arranged circularly side by side, forming a quadrate cone; aperture large, sub-quadrate, irregular; operculum composed of four valves, in pairs.--Obs. This genus differs from Conia in the structure of the shell, the latter being porous. Fig. 22, Elmineus Leachii.

ELPHIDIUM. Montf. (Conch. Syst. t. 1. p. 15.) A genus of microscopic Foraminifera.

EMARGINATED. (e, out; margo, border.) Notched or hollowed out. Applied to the edges or margins of shells, when instead of being level they are hollowed out, as the outer lip of Oliva, fig. 457, at the base, and the ventral margins of some bivalves.

EMARGINULA. Lam. (e, out; margo, border.) Fam. Calyptracea, Lam. Branchifera, Bl.--Descr. Patelliform, oblong or oval; anterior margin notched or emarginated; apex posteriorly inclined; muscular impressions wide.--Obs. Emarginula elongata, of some Authors, PARMOPHORUS of De Blainville is commonly called the Duck's bill limpet, from its shape. The Emarginulæ may be known from Patellæ and other neighbouring genera, by the notch or slit in the anterior edge. In the genus Rimula, Defr. fig. 243, this slit is near the apex, and does not reach the margin. Recent species occur in all climates, but are not numerous. Fossil species are still more rare, occurring in the Calc-grossièr, Crag and Oolite. E. fissurata, fig. 241.

ENA. Leach. A sub-genus of Bulinus. B. Lackhamensis. Mont.

ENDOSIPHONITES. A genus composed of Ammonites, having the siphon close to the body whorl, fig. 476.

ENDOTOMA. Rafinesque. A genus of microscopic Foraminifera.

ENROULEES. Lam. See CONVOLUTÆ.

ENSATELLA. Sw. A genus consisting of SOLEN ensis, Auct. fig. 60, and other species similarly curved. Genus ENSIS, Schum.