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of natural history which treats of birds ; 

 describes their structure, external and 

 internal ; and teaches their economy and 

 their uses. 



ORNITHO'LOGIST. One versed in that 

 branch of natural history which treats 

 of the habits, structure and uses of 

 birds. 



ORNITHORHY'NCHUS. (from opr/tg, a bird, 

 and puyxoc., a beak, Gr.) The platypus 

 of Shaw. The duck-bill ; an animal in- 

 digenous to New Holland, and found in 

 no other country. In this anomalous 

 animal, we have a quadruped clothed with 

 fur, having a bill like a duck, with four 

 webbed feet, suckling its young, and most 

 probably ovo-viviparous : the male is 

 furnished with spurs. The mouth of the 

 ornithorhynchus has a form of construc- 

 tion between that of quadrupeds and birds, 

 being furnished, like the former, with 

 grinding teeth at the posterior part of 

 both the upper and lower jaws, but they 

 are of a horny substance ; the mouth 

 is terminated in front by a horny bill, 

 greatly resembling that of che duck, or the 

 spoon-bill. It has also small cheek- 

 pouches. Membranes unite the toes of 

 the fore and hind-feet ; in the fore-feet it 

 extends beyond the nails, in the hind-feet 

 it terminates at the root of the nails. It 

 has also a flattened tail. It inhabits the 

 rivers and marshes. 



O'RPIMENT. (from auripigmmtum, Lat. 

 orpiment, Fr. orpimento, It.) The Arse- 

 nic sulfure jaune of Haiiy ; Arsenic sulfure 

 orpiment of Brongniart. Yellow sul- 

 phuret of arsenic, an ore of arsenic com- 

 bined with sulphur. Its colour is usually 

 lemon-yellow, which is often shining and 

 beautiful. It occurs in laminated or 

 lamellar masses ; in concretions ; and 

 sometimes in minute crystals. It is 

 principally volatilized before the blow- 

 pipe, with a white smoke, and with the 

 odour of both sulphur and arsenic, leaving 

 a small earthy residue. According to 

 Thenard it is composed of arsenic 57, 

 sulphur 43. Klaproth states his analysis 

 to be arsenic 52, sulphur 38. 



The foliated structure of orpiment, and 

 its arsenical odour, when exposed to heat, 

 distinguish it from native sulphur. It 

 occurs in veins, in various metalliferous 

 formations, in Hungary and Germany, 

 India and America. 



O'RTHITE. (from 6p0o, straight, Gr.) A 

 mineral found in the mine of Finbo, in 

 Sweden, and thus named from its being 

 always found in straight layers. 



ORTHOCE'RATA. 1 (from 6pOo, straight, 



ORTHOCE'RATITE. $ and Kt/oac, a horn, 

 Gr.) An extinct genus of polythalamous, 

 or many chambered, cephalapods, which 

 inhabited straight shells. The orthocera- 



tite resembles an ammonite unrolled, 

 having its chambers separated by trans- 

 verse septa, concave externally, and con- 

 vex internally ; the septa being pierced 

 by a siphuncle. There are many varie- 

 ties ; some upwards of two feet in length. 

 Orthoceratites are abundantly found in 

 the transition strata, appearing to have 

 been early called into existence, and at an 

 early period to have been consigned to 

 almost total destruction. Part of the 

 pavement of the palace at Hampton Court, 

 and that of the hall of University College, 

 Oxford, are composed of marble contain- 

 ing remains of Orthoceratites. Some 

 species, found in the carboniferous lime- 

 stone of Closeburn,in Dumfries-shire, are 

 nearly of the size of a man's thigh. 



ORTHO'PTERA. (from 6y9o, straight, and 

 TTTtpbv, a wing, Gr.) An order of in- 

 sects, the sixth in Cuvier's arrangement. 

 The coverings of the wings, instead of 

 being of a horny texture, are soft and 

 flexible. The wings themselves, being 

 broader than their coverings, are, when 

 not in use, folded longitudinally like a 

 fan. 



ORYCTOLO'GICAL. (from bpvKrbg, a fossil, 

 and Xoyog, discourse, Gr. ) Pertaining to 

 that part of physics which treats of 

 fossils. 



ORYCTO'LOGIST. One who studies, or is 

 versed in, that part of physics which 

 treats of fossils. 



ORYCTO'LOGY. (from opvicroc., a fossil, and 

 Xoyog, discourse, Gr.) By some persons 

 oryctognosy has been substituted for 

 oryctology, and geognosy for geology ; 

 for this there appears no valid reason, 

 and if followed, we ought, by the same 

 rule, to change metereology into metere- 

 ognosy, physiology into physiognosy, &c. 

 Oryctology is that branch of mineralogy 

 which has for its object the classification 

 of minerals ; or, in other words, it con- 

 sists in the description of minerals, the 

 determination of their nomenclature, and 

 the systematic arrangement of their dif- 

 ferent species. Cleaveland. 



OSCILLA'TION. (oscillatio, Lat. oscillation, 

 Fr. oscillazione, It.) Vibration ; the act 

 of swinging to and fro ; a movement to 

 and fro, like the swinging of the pendu- 

 lum of a clock, or waves in water. The 

 tides are oscillations of the sea. 



OSMERO'IDES MANTE'LLII. The name 

 given by Dr. Mantell to an ichthyolite of 

 the chalk formation discovered in the 

 Lewes chalk-pits. It is closely related 

 to the smelt. 



O'SMIUM. (from ocrfir], odour, Gr.) A 

 metal discovered by Tennant in crude 

 platinum, and deriving its name from the 

 strong odour emitted by some of its com- 

 pounds. 



