TUN 



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tunicated animals have no external shell 

 nor internal solid parts, but are covered 

 with a tough, elastic, homogeneous tunic, 

 in the form of an enveloping sac, with a 

 respiratory and an anal orifice. This ex- 

 terior sac is the analogue of the valves of 

 conchifera, and has the muscular fibres 

 of the lining mantle inserted into its 

 inner surface. The word is synonymous 

 with tunicaries. 



TU'NICATED. Covered with one or more 

 tunics or membranes. 



TU'RBINATED. (turbint, Fr. turbinatus, 

 from turbo, a top, Lat.) Of a spiral 

 oblong form ; in conchology, applied to 

 shells, broad at the base, and becoming 

 gradually narrower till they are pointed 

 at the apex. 



TU'RBINATED BONES. Two bones of the 

 nostrils. These are curiously folded, and 

 often convoluted in a spiral form. 



TU'RBO. (turbo, a top, Lat.) Plural, 

 turbines. A genus of marine univalves, 

 found on rocks and sea-weeds at depths 

 varying to ten fathoms. The genus turbo 

 is placed by Cuvier in the family Tro- 

 choida, and by Lamarck, in the family 

 Turbinacea. The turbo of Linnaeus 

 comprises all the species with a com- 

 pletely and regularly turbinated shell and 

 a perfectly round aperture. 



The turbo is a conoidal or slightly tur- 

 reted shell, the aperture complete, 

 rounded, and not toothed ; the margins 

 disjoined in the upper part ; the colu- 

 mella smoothed at the base. In Turton's 

 Linne one hundred and fifty-one species 

 of turbines are described, sixty-nine of 

 which are indigenous to Britain. Four 

 species of turbines have been described 

 as found fossil. 



TU'RKOIS. ) (turquoise, Fr.) A gem of 



TU'RCIUOISE. $ a blue or greenish colour, 



and opaque, found in roundish masses, 

 from the size of a pea to that of an egg. 

 The finest specimens are brought from 

 Persia, where they occur in small veins in 

 slate-clay. 



TU'RRILITE. (from turris, a tower, Lat. 

 and \i9oQ, a stone, Gr.) A spiral, tur- 

 riculated, multilocular shell ; the turns 

 contiguous and all visible. The cham- 

 bers divided by sinuous septa, pierced by 

 a siphuncle in their disks. The mouth 

 round. The shells of this genus abound 

 in the chalk marl, gait, and Shanklin 

 sand. They are extremely thin, and their 

 exterior is adorned and strengthened with 

 ribs and tubercles. The outer chamber, 

 which contained the animal, is large. 

 Professor Buckland states that turrilites 

 do not appear until the commencement 

 of the cretaceous formations, and that 

 having thus suddenly appeared, they be- 

 come as suddenly extinct at the same 

 period with the ammonites. 



TURRITE'LLA. A genus of turreted, elon- 

 gated, marine univalves, of the family 

 Turbinacea, found both recent and fossil. 

 Turritellse are commonly known by the 

 name of screw-shells. Recent turritellae 

 are found in sandy mud, at depths vary- 

 ing from five to twenty fathoms. Fossil 

 turritellse are found in the tertiary de- 

 posits. Dr. Mantell enumerates four 

 species as occurring in the London clay 

 of Sussex, and Lamarck mentions ten 

 species as discovered among the fossils of 

 Grignon, &c. 



TY'MPAN. 1 (tympanum, Lat. TV^TTOVOV, 



TY'MPANUM. $ Gr. tympan, Fr. timpano, 

 It.) A cavity or chamber of the ear. It 

 is sometimes also applied to a membrane 

 that stretches across the cavity of the 

 ear, called also the drum of the ear. 



U 



U'LNA. (ulna, Lat. from w\lvri, Gr.) 

 The cubit or large bone of the fore-arm. 

 The two bones that form the fore -arm, 

 or that portion of the upper extremity 

 situated between the elbow and the wrist, 

 are the radius and ulna ; of these the 

 ulna is the larger. 



U'LNAR. Pertaining to the ulna. 



ULTRAMARI'NE. Azure stone ; lapis la- 

 zuli. A pigment remarkable for the 

 durability of its colour. For a description 

 see Lapis Lazuli. 



U'MBEL. (umbella, Lat.) In botany, a 

 peculiar form of inflorescence : an umbel 

 consists of several flower-stalks or rays, 

 nearly equal in length, which spread from 

 one common centre, and the summits of 



which form a regular surface, either level, 

 convex, or globular ; sometimes, but 

 rarely, concave. An umbel is either 

 simple or compound : a simple umbel has 

 the stalks springing from the same part 

 of the principal one, and each bears but 

 one flower. A compound umbel has each 

 ray or stalk terminating in another set of 

 rays ; the carrot, parsnip, parsley, &c. fur- 

 nish familiar examples ofcompoundumbels. 



UMBELLA'TA. (from umbella, Lat.) The 

 name given to the partial or smaller 

 umbel of a compound umbel. 



U'MBELLATED. Having umbels ; bearing 

 umbels ; in the form of an umbel. 



UMBELLA'T^E. One of Linnaeus' natural 

 classes or orders of plants. The urn- 



