OOLITE, 



[ 555 ] 



OPERCULINA. 



OOLITE, or hoestone, is the substance 

 of oolitic rocks, aud consists of carbonate of 

 lime, partly crystallized, partly granular; 

 the granules usually include organic remains, 

 as broken shell, &c. It consists of two 

 parts, one of which, forming the matrix, is 

 mostly colourless, often crystalline, and 

 exhibits a number of round or oval cavities, 

 each of which contains a nodular granule 

 of a corresponding form. The nodides are 

 sometimes coloured, rarely hollow, and 

 often exhibit concentric rings like those of 

 calcidi, and indicative of the successive 

 deposition of layers. Sometimes a Forami- 

 nifer, but more often an organic fragment, or 

 grain of sand, forms the nucleus of the 

 grain. 



Polished sections of oolite form interest- 

 ing objects; aud where the nodules are 

 coloured and the matrix colourless, as in 

 oolite from Bristol, in which the former are 

 red, the beauty of the appearance is in- 

 creased. 



See Rocks. 



OOMY'CES, Berk, and Br.— A genus of 

 Pyrenomycetes (Ascomycetous Fungi), 

 founded on a minute plant growing upon 

 the leaves of grasses. O. carneo-allus, 

 {Sphceria carneo-alha, Libert) has pale, 

 flesh-coloured, tough receptacles 1-18" high, 

 marked with the ostioles of 3-7 perithecia 

 closely packed within it, bearing resemblance 

 to the eggs of some insects. 



BiBL. Berk, and Broome, Ann. Nat, Hist. 

 2 ser. vii. p. ISo. 



OOSPORE.— A term used to indicate a 

 spore which is impregnated before germina- 

 tion, as in CEdoffoniiwi ; and also applied to 

 the larger form of spore in Selagi^jella 

 and IsoETES. 



OPAL. — A siUceous mineral. There are 

 many varieties, thin sections of which 

 present interesting objects for the micro- 

 scope and microspectroscope. Wood opal 

 is wood petrified w ith hydrated silica, and 

 is light and not very hard. It exhibits in 

 some places vegetable structure. Other 

 opals contain the remains of substances 

 which may be of vegetable origin, or of 

 minerals which simulate such organisms. 



BiEE. Dana, Mineral. ; Slack, 31. Mic. 

 Jn. 1873, 105 ; Zirkel, Mineral. &c. 112. 

 See Agate. 



OPALI'NA, Purk. and Val.— The ani- 

 mals comprised under this title were for- 

 merly regarded as Infusoria ; but later re- 

 searches tend to show that many are im- 

 perfectly developed forms or intermediate 



stages of higher animals. They are micro- 

 scopic, oval or oblong, colourless, covered 

 with vibratile cilia arranged in regular rows. 

 Some contain a nucleus, and exhibit coa- 

 tractile vesicles ; but they do not admit 

 colouring-matters, nor have they a mouth. 

 In one form an adhesive suctorial disk has 

 been observed, and in another a hook- 

 apparatus, probably serving the same end. 

 They are parasitic vvithiu the bodies, usually 

 the intestinal canal, of earth-worms, frogs, 

 Planari<s, Naides, beneath the gill-plates 

 of Gammarus, &c. 



O. (Bursuria, F.) ranarum, is figured in 

 PL 31. fig. 47. 



BiBL. Purkinje and Valentin, De mot, 

 vibr. ; Schultze, Turhell. ; Stein, Inf. ; Cla- 

 parede et Lachmann, Etudes, 373 ; Lan- 

 kester, Qu. M. Jn. 1870, 143; Kent, Inf. 558. 



OPEG'RAPHA, Ach.— A genus of Gra- 

 phidese (Lichenaceous Lichens), gi'owing on 

 bark of trees, stones, &c. Besides their 

 linear lirellce., the fronds bear spermogonia, 

 in O. varia and O. calcarea forming black 

 spots on the surface, communicating with 

 little unilocular cavities lined with short 

 linear sterigmata bearing numerous sper- 

 matia. Several species. 



BiBL. Br. Fl. ii. pt. 1. 147 ; Tulasne, 

 Ann. Set. Nat. 3 ser. xvii. 207 ; Leighton, 

 Lich. Flora, 395. 



OPERCUL AREL'LA , Hincks, = Cam- 

 panidaria pt. (Hincks, Hyd. Zooph. 193.) 



OPERCULA'RIA, Goldfuss.— A doubt- 

 ful genus of Vorticellina, now included in 

 Epistylis. 



O. articnlata, E. Found adherent to Hy- 

 dropldlus piceus and F)ytiscus maryinalis. 

 PI. 32. fig. 25. 



O. lerberina, St. Found upon Noterus 

 crassicornis, a water-beetle. 



Other species, on Entomostraca, &c. 



BiBL. Ehr. Infus. 286 ; Stein, Lifus. ; 

 Clapai ede et Lachmann, Etudes, 111; Kent, 

 Inf. 710. 



OPERCULI'NA, D'Orb.— A Nummuline 

 Foraminifer. Shell flat, discoidal, many- 

 chambered ; spire exposed, and whorls 

 rapidly increasing in width. The shell- 

 structure of O. arabica, Carter, is described 

 at p. 330 (PI. 24. figs. 23-26), Rare in the 

 Chalk, and abundant in many Tertiaiy beds. 

 Large and plentiful in the East-Indian and 

 South seas; common, but small, in the 

 northern seas. 



BiBL. Williamson, Tr. 3Iicr. S. ii. 159 

 (" Nonionina''); Carter, Ann. N. H. 2. x. 

 101, 3. viii. 311; Carpenter, Phil. Tr.lSoQ; 



