Page:The New International Encyclopædia 1st ed. v. 15.djvu/155

* ORTHOCERAS. 124 ORTHOPTERA. versely striated. The interior of tlic shells is divich'il into eliauibers by simple transverse septa, anil (here is a median siphuncle. The members of this genus, which range from the Silurian to the Triassic periods, are of much importance as index fossils. The limits of the genus as de- lined by the majority of writers have been so broail as to include almost all of the straight- shelled Paleozoic cephalopods, and the assem- blage of species thus brouglit together was found by Hyatt and other investigators to contain species that belong more properly in a number of dill'erent families and several new genera. All of the straight-shelled forms are now classed to- gether in an artificial group as orthoeeracones, in distinction to the curved shells or eyrtocera- cones. The orthoeeracones are in general ante- ee<Ient to the cyrtoceracones in each family or race. They ajipisir first in the L'jiper Cambrian and are very aliuulant in the Ordovician rocks, where OrlluKrnin titan of the Black fiiver lime- stone, with a length of about ten feet, is the largest known form of this group of cephalopods. During the Ordovliian the orthoeeracones gave rise to several derived genera of curved and coiled shells, and to shells with peculiarly restricted apertures. 8omc of these forms gave' rise to side lines of evolutiim that flourished for variable periods of time, such as Cyrtoeeras, Gyroeeras, Lituites, I'hraginoceras, and Ascoreras. Xau tilus itself, which has persisted to the present day, was derived in early Ordovician times from one of these orthoeeracones through a curved .shell like Cyrtoeeras. During the Silurian, De- vonian, and Carboniferous periods the ortho- eeracones diminish in both size and number, and they disappear during the Trias. The deriva- tion of Belemnites of the IVIesozoie from some Paleozoic orthoeeracones is considered bv some authors to have taken place through the forma- tion by the orthoceras of a heavy deposit of lime upon the apical portion of its shell, this serving as a post to anchor the shell in an upright posi~- tion in the mud of the sea bottom. Consult : riuedemann. ''Professor .Taekel's Theses on the Alode of Existence of Orthoceras and Other Ce- phalo))ods," Amrrican GrnJoqi.it. vol. xxxi. (Min- neapolis. 190.'?) : Von Zittel and Eastman. Text- hook uf I'dlrontoloftji, vol. i. (New York and Lon- don. 1000). See Cephalopoda; Nautilu.s. OR'THOCLASE (from Gk. 6pe6s, orthos, straight, correct + Kaffts, klasis. fracture, from Kap, 1.1(1 II. to break). One of the monoclinio feldsi)ars. coni])osed of potassium-aluminum sili- cate. It has a vitreous lustre, and is either color- less or white, though occasionally light yellow or red, and sometimes green. It usually "occurs in crystalline rocks, and is an essential "constituent ,of granite, gneiss, syenite, pori)hyry, etc. The several varieties of oithoclase include riduhiriii. a transparent or translucent variety that shows when polished chatoyant or j>early reflections, the best varieties of which are cut into gems and are known as 'moonstones:' nventuriiie. a similar variety with red and yellow internal reflections, due to minute scales of occluded minerals, the green varieties being known as 'sunstnncs;' pcrthite, a flesh-red variety oontainin? layers of albite and often yielding bright goldemyellow re- flections; and vnriolUe. a dark-greeii variety, which takes its name from its supposed power to cure smallpox. ORTHO'EPY (i;k. opOoiirtia, orlliocpeia, cor- rect speaking, from 6p$oeireii/, ortliocjirin. to speak correctly, from 6p$(is, oiltios, straight, correct -|- ?iros, epos. word). That jiart of granunar which treats of the correct pronunciation of the words of a language. ORTHOGENESIS (Gk. dpDos, or//ios, straight, correct + -y^vcffn. yeiiesis, origin). Generation according to ordinary processes, as distinguished from such aberrant courses of development as parthenogenesis, alternation of generations, and other sjiccial modes. ORTHOGONAL. See Pbojection. ORTHOG'RAPHY (Lat. orthographia, from Gk. 6peoypa<pia. c'orrect writing, from iptids, orllws, straiglit, correct + ypd<peir. gniphein, to write). The art of writing words correctly, as regards spelfing. The word is seldom used in an absolute sense — that is, with the meaning of spelling which is scientifically correct — since out- side of the discussions of phonetists (see Pho- netics) such spelling does not exist; it ordinari- ly signifies merely the art of spelling in accord- ance with accepted or prevailing usage, and also such customary spelling itself. See Spelling and SPELLI.NU ReFOHIU. ORTHOGRAPHY, Figures of. Deviations from the ordinary accepted spelling of words. They are three in number; arcli<.ii.>,-iii, crasift, and miiiicsis. Areliaism consists in spelling words ac- cording to a usage wOiich is obsolete or ob.soles- eent, as if one should write, "The gret Kyiig hathe tifty fair damysclles alle nuigdciics." So Vergil has olli for illi, Horace duellum for helium. Cri- sis (Gk. Kpdffis, a mixing) in Greek grammar denoted the mixing of two words by the coales- cence of their final and initial vovvels into one long syllable. Thus to airi became raird. The occurrence of crasis is indicated by the coro- "i.« (') placed over the vowel or diphthong of the resulting long syllable. In Latin grammar the term crasis was applied to the union of any two vowels into a long vowel or diphthong, and so became synonymous with contraction. Examples of crasis in Latin are cogo (for eoniio), nil (for nihil) . cors (ior cohors) . Mimesis (Gk. m'm';o-«», imitation) consists in the representation of the improper pronunciation of words by means of false spelling. Mimesis is common in works which profess to represent the speech of the illite- rate, or which introduce characters who use dia- lect, or negro speech. OR'THOP^'DICS (from Gk. dpBb,. orthos, straight, correct + wah, pais, child). The pre- vention or correction of deformity in the human body, especially in children. See Clubfoot; Knock-Knee; Leo; Pott's Disease; Deformi- ties. ORTHOP'ODA (Neo-Lat. nom. pi., from Gk. dpebi, orthos. straight, correct + jroSs, poM.s, foot). An order of dinosaurs, in the system of Gadow, embracing the groups Stegosauiia and Ornitho- poda of Marsh. See the sections on these groups under Dixosauria. ORTHOP'TERA (Neo-Lat. nom. pi., from Gk. dpBbTTTtpoi, having upright wings, from ipS6i, orthiis, straight, con-ect + wTcpdv, pteron, wing). A large and important group of insects comprising the forms known as the straight- winged insects, and including the grasshoppers or true locusts, long-horned grasshoppers (in-