Part 74

TRIGONACEA. Lam. A family belonging to the order Conchifera Dimyaria, containing the genera Trigonia and Castalia, the latter of which ought to be removed to the Nayades. Fig. 139, 140.

TRIGONAL. Triangular, having three sides.

TRIGONELLA. Humph. MACTRA, Auct.

TRIGONIA. Brug. ([Greek: trigônon], trigonon, triangular.) Fam. Trigonata, Lam. Camacea, Bl.--Descr. Equivalve, inequilateral, transverse, sub-trigonal, costated and granulated without, pearly and iridescent within, denticulated on the inner margin, rounded anteriorly, truncated posteriorly; hinge with four oblong, compressed, diverging teeth in one valve, receiving between their grooved sides, two similar teeth in the other; ligament external, thick; muscular impressions two in each valve.--Obs. Only one recent species of this marine genus is known, the T. pectinata, which comes from New Holland; and was formerly so rare, that a much worn odd valve has been sold for a considerable sum. It is of a brilliant pearly texture within, tinged with purple or golden brown. Fossil species occur in Lias, upper and lower Oolite, and Green-sand. T. Pectinata, fig. 139.

TRIGONOSEMUS. König. A genus composed of species of TEREBRATULA, Auct. which have one valve produced into a beak, perforated, or as it were truncated at the apex. T. lyra, fig. 208, differing from Terebratula lyra, Lam.

TRIGONOSTOMA. A sub-genus of Helix, with a trigonal aperture. Gray's Turton, p. 139.

TRIGONOTRETA. König. A genus composed of species of Terebratula, Auct. which have the hinge of the larger valve produced into a triangular disc, divided by a triangular foramen in the centre. Spirifer, Sowerby, belongs to this genus. Fig. 214, 215.

TRILOBATE. ([Greek: Treis] three; [Greek: lobos], division, lobe.) Divided into three lobes or principal parts. Ex. Malleus, Fig. 165.

TRILOCULINA. D'Orbigny. A genus of microscopic Foraminifera.

TRIPARTITE. (Tripartitus) composed of or divided into three separate parts.

TRIPHORA, or TRISTOMA. Deshayes. A genus composed of small reversed species of CERITHIUM, Auct. which have the anterior canal closed at the anterior of the aperture, but opened at the extremity, and a small tubular opening on the upper part of the whorls, making three openings on the body whorl. This genus stands in the same relation to Cerithium as the Typhis to Murex. Fig. 375 in the old plates, and fig. in the new plates.

TRIPLEX. Humph. MUREX, Linn.

TRIPLODON. Spix. HYRIA, Auct.

TRIPTERA. Quoy et Gaimard, CUVIERA, Fer. Described in the Voyage de la Coquille, and represented as a molluscous animal destitute of a shell.

TRIQUETRA. Bl. Triangular species of VENUS Auct.

TRISIS. Oken. ARCA tortuosa, Auct.

TRISTOMA. Described as TRIPHORA.

TRITON. Auct. Fam. Siphonostomata, Bl. Canalifera, Lam.--Descr. Oblong or oval, thick, ribbed or tuberculated, with discontinuous varices placed at irregular distances; spire prominent, mammillated; aperture round or oval, terminating anteriorly in a generally long, slightly raised canal; columellar lip granulated or denticulated; outer lip thickened, reflected, generally denticulated within; epidermis rough; operculum horny.--Obs. However nearly allied the Tritons may appear to be to the Murices and Ranellæ there are still to be traced in the shells of each of those genera, several constant and well marked distinctions, by which they maybe at once recognized. In the Ranellæ, the varices run in two rows along the spire; in the Murices, they form three or more rows; but in the Tritons, they do not follow each other, i.e. they do not occur in the same part of each volution. The large species of Triton, are sometimes used as trumpets. The Tritons are brought from the Mediterranean, Ceylon, the East and West Indies, and South Seas. Fig. 398 to 401.

TRITONIDEA. Sw. A genus of "Buccininæ," Sw. thus described: "Shell bucciniform, but the basal half is narrowed, and the middle more or less ventricose; spire and aperture equal. Pillar at the base with two or three obtuse and very transverse plaits, not well defined; outer lip internally crenated and with a superior siphon; inner lip wanting, or rudimentary." This genus is the same as the one first distinguished by Mr. Gray under the name of Pollia. We do not regret the discovery made by Mr. Swainson of that name being previously occupied for a genus of Lepidopterous Insects. Fig. 415, represents Tritonidea articularis. (Pollia, Gray.)

TRIVIA. Gray. A genus composed of those small species of CYPRÆA, Auct. which are characterized by small ridges on the dorsal surface, and have the anterior of the columella internally concave and ribbed. C. Pediculus. Auct. fig. 449, 450.

TROCHATELLA. Sw. A sub-genus of Helicinæ, consisting of those species which are acute and trochiform.

TROCHIA. Sw. A genus of the family Buccininæ, thus described: "shape intermediate between Purpura and Buccinum; whorls separated by a deep groove; inner lip when young, depressed, when adult, thickened, convex and striated; basal canal very small. T. sulcatus. E. M. 422. f. 4." Sw. Malac. p. 300.

TROCHIDON. Sw. A sub-genus of "Trochinæ," Sw. Lardn. Cyclop. Malac. p. 351.

TROCHILÆA. Sw.? PILEOLUS, Auct.

TROCHURUS. Humph. MONODONTA. Lam.

TROCHUS. Auct. (A top.) Fam. Turbinacea, Lam. Goniostomata, Bl.--Descr. Turbinated, thick, striated, tuberculated or smooth; spire elevated, conical, consisting of numerous whorls; under surface discoid; aperture more or less depressed in an oblique direction, generally angular; columella arcuated, more or less prominent at its union with the outer lip, contiguous to the axis of the shell; operculum horny, orbicular, with numerous whorls.--Obs. Lamarck distinguished this genus from Turbo by the general form, which is more conical, and the aperture, which is angulated, while that of Turbo is rounded. Monodonta or Odontis is only separated on account of the notch at the termination of the columella. But these characters glide so imperceptibly from one genus to the other, that there is no line of demarcation to be found but in the operculum. Accordingly, Sowerby (in Gen. of Sh. 37.) has stated his reasons for considering as Trochi, all the species which have horny opercula; and as Turbines, all those which have testaceous opercula. Fig. 358 to 360. The Trochi are found in all climates.

TROPÆUM. Sow. CRIOCERATITES.

TROPHON. Montf. MUREX Magellanicus, Auct. and several other species which belong more properly to Fusus than to Murex.