OPE 



OPH 



split on a sudden change of temperature : 

 it is principally used for necklaces, ear- 

 rings, and finger-rings. The most beau- 

 tiful opals known are in the Imperial 

 cabinet of Vienna ; one is five inches long 

 and two and a half in diameter : another 

 is of the size and nearly of the shape of a 

 lien's egg. The noble opal consists of 

 silica and water in tlie proportion of 9 to 

 1. Specimens of the common and semi- 

 opal have been analysed and found to con- 

 sist as follows : 



Common Opal. Semi Opal. 



Silica 9875 43.50 



Alumina .... 0.1 0.0 



Oxide of iron . . 0.1 47. 



Water 0.0 7-5 



Loss 



98.95 

 1.05 



100 



98.00 

 2 



100 



OPATRUM, in natural history, a ge- 

 nus of insects of the order Coleoptera. 

 Antennze moniliform, thicker towards the 

 tip ; head projecting from a cavity in the 

 thorax ; thorax a little flattened, margin- 

 ed ; shells immarginate, longer than the 

 abdomen. There are twenty-eight spe- 

 cies, O. sabulosum, is brown, shells with 

 three indented raised lines ; thorax emar- 

 ginate. Inhabits Europe and America, on 

 sand. 



OPERA, a dramatic composition set to 

 music, and sung on the stage, accompa- 

 nied with musical instruments, and en- 

 riched with magnificent dresses, ma- 

 chines, and other decorations. 



OpERA-^-Zrtss, in optics, so called from 

 its use in theatres, &c. it is sometimes 

 called a " diagonal perspective" from its 

 construction. It consists of a tube about 

 four inches long, in each side of which 

 there is a hole exactly against the mid- 

 dle of a plane mirror, which reflects the 

 rays falling upon it to the convex glass, 

 through which tney are refracted to the 

 concave eye-glass, whence they emerge 

 parallel to the eye at the hole in the 

 tube. This instrument is not intended to 

 magnify objects more than about two or 

 three times. The peculiar artifice is to 

 view a person at a small distance, so that 

 no one shall know who is observed: for the 

 instrument points lu a different object 

 from that which is viewed ; and as there 

 is a hole on each side, it is impossible to 

 know on which hand the object is situat- 

 ed, which you are looking -at. 



OPERCULARTA, in botany, a genus 

 of the Telrandria Monogynia class and 

 order. Essential character : flower com- 

 pound; calyx common, one-leafed, un- 

 equally toothed, closed by a common re- 

 ceptacle, flowering above, seeding below, 

 falling when ripe. There are three spe- 

 cies. 



OPHIDIUM, in natural history, a ge- 

 mis of fishes of the order Apodes. Gene- 

 ric character : the head rather nuked ; 

 teeth in the jaws, palate, and throat ; gill 

 membrane seven-rayed ; body in the form 

 of a sword. There are four species. We 

 shall notice only O. barbatum, or the 

 bearded Ophidium : this is generally 

 about eight inches long, and is a native 

 of the Adriatic and Mediterranean Seas, 

 and is not much valued as food. It sub- 

 sists on small fishes and crabs. 



Ol'HIOGLOSSUM, in botany, adder's 

 tongue, a genus of the Cryptogamia Fili- 

 ces class and order. Natural order of 

 Filices, or Ferns. Generic character: 

 capsules numerous, connected by a mem- 

 brane into a distich spike, subglobular, 

 when ripe opening transversely, without 

 any elastic ring ; seeds very many, ex- 

 tremely minute. There are nine species. 



OPHIORHIZA, in botany, a genus of 

 the Pentandria Monogynia class and or- 

 der. Natural order of Stellatx. Gentia- 

 nae, Jussieu. Essential character: coroU 

 la funnel-form ; germ bifid ; stigmas 

 two; fruit two-lobed. There are three 

 species. 



OPHIOXYLUM, in botany, serpentine 

 wood, a genus of the Polygamia Monoecia 

 class and order. Natural order of Apoci- 

 neae, Jussieu. Essential character : her- 

 maphrodite, calyx five-cleft ; corolla five- 

 cleft, funnel-form; stamens five; pistil 

 one : male calyx bifid ; corolla five-cleft, 

 with a funnel-form moutii ; nectary cylin- 

 dric ; stamens two. There is but one 

 species ; -viz. O. serpentinum, scarlet- 

 flowered ophioxylum, a native of the East 

 Indies. 



OPHIRA, in botany, a genus of the Oc- 

 tandria Monogynia class and order. Na- 

 tural order ot Onagrae, Jussieu. Essen- 

 tial character: involucre two-valved, 

 three-flowered ; corolla four-pet ailed, su- 

 perior ; berry one-celled. There is but 

 one species ; viz. O. stricta, a native o 

 Africa. 



OPHRYS, in botany, a genus of the 

 Gynamlria Dianrlria class and order. Na- 

 tural order of Orchidese. Essential cha- 

 racter: nectary somewhat keeled under- 

 neath. There are thirty-four species. 

 These plants are of the same naturaJ ge- 



