Part 76

10. MONODONTA or ODONTIS. A notch and prominent point at the lower part of the aperture. Fig. 366.

11. LACUNA. With an umbilicus. Fig. 364.

12. TURRITELLA. Elongated, screw-shaped. Fig. 369 to 371.

TURBINATED. (Turbo, a top,) Top-shaped. The term is applied generally to those shells which are large at one extremity, and narrow to a point at the other. Ex. Trochus, fig. 358; Turbinellus, fig. 382.

TURBINELLUS. Auct. (A little top.) Fam. Canalifera, Lam. Siphonostomata, Bl.--Descr. Turbinated, thick, wide near the apex, generally tuberculated; spire short, depressed, mammillated; aperture rather narrow, terminating anteriorly in an open canal; outer lip thickened within; columella having from three to five prominent, compressed, transverse folds. The species of this genus are mostly tropical.--Obs. The Turbinelli are a well marked genus of marine shells, the species of which are numerous. No fossil species are known. The genus Cancellaria makes the nearest approach to Turbinellus in some characters, but may be distinguished by the roundness of its form, the raised lines inside the outer lip, and the obliquity of the folds on the columella. Fig. 382 to 384.

TURBO. Auct. (A top.) Fam. Cricostomata, Bl. Turbinacea, Lam.--Descr. Turbinated, solid, ventricose, generally grooved or tuberculated; spire short, pointed; aperture generally rounded, sub-effuse anteriorly, entire; operculum shelly, solid, incrassated on the outer side, horny and sub-spiral on the inner side. The Turbines are mostly tropical.--Obs. The only certain means of distinguishing this extensive genus of marine shells from Trochus, is the operculum, which in the latter genus is horny, spiral, and composed of a great number of whorls. The Trochi, however, are in general more conical, and flatter at the under side of the whorls, and this constitutes Lamarck's distinction between the genera. T. setosus, fig. 368.

TURGID. (Turgidus.) Puffed up, swollen, inflated. This term is applied synonymously with Ventricose.

TURRICULA. Humph. MELANIA, Auct.

TURRICULACEA. Bl. The seventh family of the Order Polythalamacea, Bl. containing the genus Turrilites, fig. 483.

TURRILITES. Lam. (Turris, a tower; [Greek: lithos], a stone.) Fam. Turriculacea, Lam. Ammonacea, Bl.--Descr. Chambered, turrited, spiral; septa sinuous and lobate, perforated by a siphon; aperture rounded, with the outer lip expanded. This genus, which is distinguished from the other Ammonacea by having the spire produced, i. e. not being convolute, consists of several species, occurring only in chalk-marl. Fig. 483.

TURRIS. Montf. A genus composed of those species of MITRA, Auct. which have the whorls angulated, with the aperture lengthened and undulated.

TURRITED. The spire of an univalve shell is said to be turrited when the whorls of which it is composed are regulated so as to have the appearance of little turrets rising above each other, as in Mitra, fig. 431.

TURRITELLA. Lam. (A little tower.) Fam. Turbinacea, Lam. Cricostomata, Bl.--Descr. Turrited, elongated, generally grooved spirally; spire pointed, consisting of numerous whorls; aperture rounded or angulated; inner and outer lips thin, confluent anteriorly; operculum horny.--Obs. The shells composing this well defined genus, are commonly called screws, a name to which the spiral grooves of most of the species seems to entitle them. Fig. 370, T. imbricata.

TYMPANOSTOMA. Schum. (Timbrel mouth.) POTAMIS, Brongn.

TYPHIS. Montf. A genus composed of MUREX tubifer, Auct. and other similar species, which have the canal closed and a perforated tube between each varix on the angulated part of the whorls. Besides the fossil species originally described, there are now five species known, which are figured in part 200, of the Conchological Illustrations by the Author. Typhis tubifer, fig. 397.

ULTIMUS. Montf. (The last.) A genus composed of OVULUM gibbosum, Auct. fig. 443, and other species in which the canals are not distinctly defined, nor elongated. This fanciful name is given to the genus on account of its being described in the last page of the book.

UMBILICATED. (Umbilicatus.) Having an umbilicus, as Nautilus umbilicatus.

UMBILICUS. (A navel.) The hollow formed in spiral shells when the inner side of the volutions do not join each other, so that the axis is hollow. The umbilicus is marked with the letter u in Helix algira, fig. 279. The term is also used to express any small, neat, rounded hollow.

UMBO. (The boss of a buckler or shield.) The point of a bivalve shell above the hinge, which constitutes the apex or nucleus of each valve, from which the longitudinal rays diverge, and the lines of growth, commencing at the minutest circle, descend in gradually enlarging concentric layers to the outer margin. The umbones will be marked with the letter u, in Cytherea, fig. 117.

UMBRELLA. (A little shade.) Fam. Semiphyllidiana, Lam. Patelloidea, Bl.--Descr. Patelliform, sub-orbicular, compressed, rather irregular; apex slightly raised, placed near the centre; margin acute; internal surface with a central, callous, coloured disc, surrounded by a continuous, irregular muscular impression.--Obs. This genus is known from Patella, by its continuous muscular impression. It is commonly called the Chinese Umbrella shell. There are but two species at present known; the U. Mediterranea, and the U. Indica, fig. 233.

UNDATED. (Unda, a wave.) Waved.

UNDULATED. (Undulatus.) Minutely waved.

UNGUICULATED. (Unguis, a nail or hoof.) An unguiculated operculum is one in which the layers are disposed laterally, and the nucleus constitutes part of the outer edge.

UNGULINA. Daud. (Ungula, a nail or claw.) Fam. Mactracea, Lam. Conchacea, Bl.--Descr. Equivalve, sub-orbicular, sub-equilateral, with margins entire, simple, closed all round; hinge with one short, sub-divided cardinal tooth in each valve, and a very minute additional tooth in one valve, an oblong ligamentary pit divided into two portions, one of which receives the cartilage, the external ligament is immediately below the umbones; muscular impressions, two in each valve, oblong; impression of the mantle entire. U. transversa, fig. 88. Coast of Africa.

UNI-AURICULATED. Having one AURICLE. See AURICULATED.

UNICORNUS. Montf. MONOCEROS, Auct.

UNIO. (A pearl.) Fam. Nayades, Lam. Submytilacea, Bl.--Descr. Inequilateral, equivalve, regular, free, pearly within, covered by a smooth epidermis without; umbones prominent, generally corroded; muscular impressions two in each valve, lateral, distant; the anterior composed of several small divisions; hinge varying in age, species, and individuals.--Obs. The above description is framed so as to include all the genera of the Lamarckian Nayades, together with Castalia, which are placed in the family Trigonacea, they are all fresh-water shells, commonly called fresh-water muscles. The distinctions of the various genera into which they have been divided, will be found in their respective places, and under the name Nayades. They are all represented in figures 140 to 152. Of these fig. 145 to 148, are more generally considered as forming the genus Unio.

UNIOPSIS. Sw. A sub-genus of Alasmodon. Sw. p. 382.