TUB 



[448 ] 



U M B 



where they occur in small veins in 

 slate-clay. 



TU'RBJLITE. (from turns, a tower, 

 Lat. and X/009, a stone Gr.) A 

 spiral, turriculated, multilocular 

 shell ; the turns contiguous, and all 

 visible. The chambers divided by 

 sinuous septa, pierced by a siphun- 

 cle 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 ani- 

 mal, is large. Buckland states 

 that turrilites do not appear until 

 the commencement of the cretaceous 

 formations, and that having thus 

 suddenly appeared, they become as 

 suddenly extinct, at the same period 

 with the ammonites. De La Beche 



says "aturrilitehasbeen mentioned, 

 though with doubt, as occurring in 

 the coral rag of the north of France. 

 Several species are enumerated as 

 having been discovered in the cre- 

 taceous group." 



TUBEITE'LLA. A genus of turreted, 

 elongated, marine univalves, of the 

 family Turbinacea, found both re- 

 cent and fossil. Turritellae are 

 commonly known by the name of 

 screw- shells. Eecent turritellse are 

 found in sandy mud, at depths 

 varying from five to twenty fath- 

 oms. Fossil turritella3 are found 

 in the tertiary and secondary de- 

 posits. 



TY'MPAN. ) (tympanum, Lat.) A 

 TY'MPANUM. ) cavity or chamber of 

 the ear. It is sometimes also ap- 

 plied to a membrane that stretches 

 across the cavity of the ear, called 

 the drum of the ear. 



U 



U'LNA. (ulna, Lat. from u>XeV?/, Gr.) 

 The cubit or large bone of the 

 fore-arm. 



ULTBAMAEI'NE. Azure-stone ; lapis 

 lazuli. A pigment remarkable for 

 the durability of its colour. See 

 Lapis Lazuli. 



U'MBEL. (umlella, 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 com- 

 pound: a simple umbel has the 

 stalks springing from the same part 

 of the principal one, and each bears 

 but one flower. A compound um- 

 bel has each ray or stalk termina- 



ting in another set of rays: the 

 carrot, parsnip, parsley, &c., fur- 

 nish familiar examples of compound 

 umbels. 



UMBELLA'T^!. One of Linnaeus' natural 

 classes or orders of plants. The 

 umbellatse are plants whose flowers 

 grow in umbels, with five petals, 

 and two naked seeds, joined at top 

 and separated below. The parsley, 

 fennel, &c., are examples. 



UMBELLI'FEILE. A large order of 

 plants, characterized by their flowers 

 being in umbels. Calyx entire or 

 five-toothed. Petals five, usually 

 inflexed at the point. Stamens 

 five, alternate with the petals. 

 Ovary two -celled. Fruit consisting 

 of two carpels, separable from a 

 common axis. Seed pendulous. 

 Herbaceous plants with fistular 

 stems. 



