L I 



[324] 



L 



tuents are silica 63-37, alumina 

 25-86, soda 11'77. 



O'UVA. (olwa, an olive, Lat.) So 

 named from the oblong and ellip- 

 tical shape of the shell. A marine 

 suhcylindrical univalve; aperture 

 narrow, long, and emarginated 

 opposite to the spire, which is 

 short ; the plicae of the columella 

 are numerous, and resemble striae ; 

 whorls sulciform. The shells of 

 this genus are very beautiful, and 

 display a great variety of rich 

 markings and splendid colours. 

 Recent olivae are found at depths 

 varying to twelve fathoms, in mud, 

 sandy mud, coarse sand, &c. They 

 are also caught by fishing lines. 

 Fossil olivae are found in the cal- 

 caire grossier, and London clay. 

 Several species have been described. 



OLI'VENITE. An ore of copper of an 

 olive-green colour. It consists of 

 oxide of copper 63 '0, phosphoric 

 acid 28-6, water 8-4. 



O'LIVINE. The prismatischer chryso- 

 lithe of Mohs; peridot of Haiiy; 

 olivin of Werner. A mineral, 

 generally of an olive-green colour, 

 from which circumstance it obtains 

 its name : it is sometimes of an 

 asparagus green, or yellowish green. 

 Occurs in distinct granular concre- 

 tions, or in rounded masses. 

 Structure foliated. Fracture im- 

 perfectly conchoidal. Lustre shin- 

 ing, translucent, and, sometimes, 

 transparent. Its constituents are, 

 silex 50-0, magnesia 8 7' 5, oxide 

 iron 12-0, lime 0*5. It is found 

 in basalt, and is a constituent of 

 many lavas. 



O'MBRIA. (from opppio*, rain, Gr.) 

 Fossil echini, to which the name of 

 ombria has been given, from a sup- 

 position that they fell from heaven 

 in the midst of heavy rain ; they 

 are of a rounded form, and have 

 been compared to turbans. 



OME'NTUH. (omeutum, Lat.) The 

 caul. 



OMNI'VOEOUS. (from omnis, all, and 



voro, to devour, Lat.) Animals 

 which eat food of all kinds. 



O'MOPLATE. (from w^o?, the shoulder, 

 and TrXaTi*?, broad, Gr.) The scap- 

 ula, or shoulder-blade. 



O'NCHVUS. A genus of sharks, belong- 

 ing to the sub-family of Hybodonts. 

 The genus onchus, says M. Agassiz, 

 is easily distinguished. It em- 

 braces certain cartilaginous fishes, 

 the dorsal spines of which only 

 have been discovered. The dorsal 

 fins are large at their base, very 

 much bent backwards, narrowing 

 rapidly towards the superior end, 

 furrowed along the whole of their 

 surface by grooves parallel to the 

 posterior margins, between which 

 pretty strong ribs rise up, which so 

 terminate as to give the anterior 

 edge a toothed aspect. The onchus 

 arcuatus is the species thus de- 

 scribed, and is the largest species 

 of the old red system, though in- 

 ferior in size to some species of the 

 carboniferous limestone. Murchi- 

 son. Teeth of the onchus have 

 been found in the lias, at Lyme 



ONTO'LOGY. The science of organic 

 beings; divided into zoology, the 

 science of animals; botany, the 

 science of vegetables ; or again 

 specifically divided into Cainon- 

 tology, the science of now living 

 organic beings, and Palaeontology, 

 the science of extinct organic bodies. 

 Jukes. 



O'NYX. (from oWg", Gr. a nail, onyx, 

 Fr.) The quartz agathe onyx of 

 Hatiy. A variety of calcedony 

 having different colours arranged 

 in distinct parallel stripes or zones, 

 and consisting of alternate layers 

 of white and brown calcedony. 

 The onyx is used by lapidaries in 

 the formation of cameos. 



O'OLITE. (from woi>, an egg, and 

 X/009, a stone, Gr. oolites, Fr.) The 

 Calcaire de Jura, Calcaire Juras- 

 sique of the French ; the Oolithen- 

 bildung, Jurakalk of the Germans. 



