A Conchological Manual by George Brettingham Sowerby (best interesting books to read txt) 📕

   its commencement in the next. The varices of Triton, occurring in

   different parts of the whorls, do not form the continuous ridges which

   characterize the generality of the Ranellæ.

   DISCORBITES. Lam. A genus of microscopic Foraminifera.

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

 distant when they are remote from the umbones.

   DIVARICATED. Diverging, meeting in a point, as the teeth on the hinge

   of Placuna, fig. 184.

   DOLABELLA. Lam. (Dim. from _Dolabra_, a hatchet.) _Fam._ Aplysiacea,

   Lam. and Bl.--_Descr._ Hatchet-shaped, arched, covered with a horny

   epidermis; posteriorly attenuated, thickened, sub-spiral, anteriorly

   plane, broad, thin; posterior margin reflected.--_Obs._ The two or

   three species of Dolabella known are inhabitants of the Indian Ocean.

   They were placed by Linnæus in his very convenient genus Bulla, under

   the name B. dubia. Fig. 255, Dolabella Rumphii.

   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,

   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.

   ENSIS. Schum. SOLEN ensis, Auct. and similar species.

   ENTALIS. Defr. DENTALIUM duplicatum, Bl. PHARETRIUM, König. This genus

   is described as a small tube, within a larger one, the smaller

   extremity of the inner tube projecting beyond that of the outer one.

   Deshayes, who describes this genus, expresses a conviction that the

   soft parts of the animal must be entirely different from those of the

   animal of Dentalium. The genus PHARETRIUM, as described by König in his

   "Icones Fossilium Sectiles," is evidently identical with Entalis. It is

   placed by him in the family of Pteropoda, but being a fossil shell,

   there is some difficulty in finding its place in the system. See

   plates, fig. 3.

   ENTELLITES. Fischer. A genus composed of species of TEREBRATULA,

   SPIRIFER, and PRODUCTUS, Auct. having the hinge large and the umbones

   short. ORTHIS? Dalman.

   ENTIRE. (Integra.) Not interrupted, not emarginated. The peritrême of a

   univalve shell is said to be entire when not interrupted by canals or

   by the body whorl. _Ex._ Cyclostoma, fig. 304. The palleal impression

   is entire, when continued without interruption, or without a sinus.

   ENTOMOSTOMATA. Bl. The second family of the order Siphonibranchiata,

   Bl. The shells of this family are described as differing but little

   from those contained in the family of Siphonostomata of the same

   author, both with regard to the soft parts, and their testaceous

   covering. This family partly answers to the Purpuriferæ in the system

   of Lamarck, and contains the genera Subula, Cerithium, Melanopsis,

   Planaxis, Terebra, Eburna, Buccinum, Harpa, Dolium, Cassidaria, Cassis,

   Ricinula, Cancellaria, Purpura, Concholepas.

   EOLIDES. Montf. A genus of microscopic Foraminifera.

   EPIDERMIS. ([Greek: Epi], _epi_, over or upon; [Greek: derma], _derma_,

   skin.) The fibrous, horny, external coating of shells, called by the

   French, "_Drap marin_," or marine cloth. Lamarck objects to the name

   Epidermis because he does not consider the substance as answering to

   the cuticle or scarf skin of the human body, but more analogous to the

   nails and hair. Gray calls it the PERIOSTRACUM, from the membranous

   skin covering the bones of quadrupeds.

   EPIPHRAGM. The membranaceous or calcareous substance by which some

   species of molluscs close the aperture of the shell, when they retire

   within it to hibernate. When the animal wishes to come forth from his

   hiding-place, again to breathe the air, the edges of the Epiphragm are

   detached by a chemical process, so that it drops off. The name

   Hibernaculum has also been given to this covering. It must not be

   confounded with the operculum, which is a permanent portion of the

   shell, and is used as a door, fitted to the foot of the animal and

   moved at will to open or close the aperture of the shell, whereas the

   Epiphragm is produced for the occasion from a mucous secretion of the

   animal and dissolved at the edges when no longer wanted, when it drops

   off.

   EPISTYLA. Sw. A subgenus of the genus HELIX. E. conical. Sw. Helix

   Epistylium, fig. 281.

   EPONIDES. Montf. A genus of microscopic Foraminifera.

   EQUILATERAL. (Æquus, equal; latus, side.) Equal-sided. A term applied

   to bivalve shells, when a line drawn down perpendicularly from the apex

   would divide the shell into two equal parts. _Ex._ Pectunculus pilosus,

   fig. 134.

   EQUIVALVE. (Æquus, equal; _valva_, a valve.) A term applied to a

   bivalve shell when the valves are equal to each other in dimensions.

   ERATO. Risso. _Fam._ Convolutæ, Lam.--_Descr._ Ovate, more or less

   angulated, smooth or granulated, with a dorsal scar; spire short;

   aperture large, angulated, emarginated; columella