RAPHIGNATHUS 



[ 549 ] 



RED SNOW. 



RAPHIGNATHUS, Duges. A genus of 

 Arachnida, of the order Acarina, and family 

 Trorabidina. 



Char. Palpi with an indistinct claw; 

 mandibles represented by two short setae 

 inserted upon a fleshy bulb, concealed by a 

 broad labium; body entire; coxae contigu- 

 ous; legs but little attenuate at the ends, 

 anterior longest, last joint longer than the 

 others. 



R. ruberrimus (PL 2. fig. 35 a, labium 

 with mandibles and a palp ; b, a mandible). 

 Body oval, slightly depressed, smooth, and 

 almost free from hairs, rostrum forming a co- 

 nical process; eyes two, dark red, one on each 

 side at the anterior part of the body ; labium 

 triangular, concave ; setae accompanied by a 

 more slender hair-like process ; palpi large, 

 inflated, claw of the 4th joint very short. 

 Size minute ! 



Found under stones and on plants. 



T. hispidum. Form of that of the pre- 

 ceding; body velvety, with two posterior 

 papillae. 



BIBL. Duges, Ann. des Sc. nat. 2 ser. i. 22, 

 ii.55; Gervais, Walckenaer's Apter. iii. 172. 



RATTULUS, Lamarck. A genus of Ro- 

 tatoria, of the family Hydatinaea. 



Char. Eyes two, frontal; tail-like foot 

 simply styliform; neither cirrhi nor fins 

 present. 



Teeth indistinct. 



R. lunaris (PI. 35. fig. 22). Eyes distant 

 from the anterior margin ; foot decurved, 

 lunate. Aquatic ; length 1-288". 



BIBL. Ehrenberg, In/us, p. 448. 



REAGENTS. See INTRODUCTION, pp. 

 xxxvii and xl. 



REBOUILLIA, Raddi. A genus of Mar- 

 chantiacese (Hepaticaceae), founded on the 

 Marchantia hemisph&rica, Linn., character- 

 ized by the conical or flattened, 1-5-lobed 

 stalked receptacle (fig, 621 ), the perigone 



Fig. 622. 



Rebouillia hemisphaerica. 



Female receptacles, with the perigone burst. 



Fig. 621, seen from above ; fig. 622, from below. 



Magnified 2 diameters. 



being adherent to the lobes of the receptacle 

 on the under side, opening by a slit (fig. 



622) ; perichaete none, and the globose spo- 

 range bursting irregularly. The antheridia 

 are imbedded in sessile, crescent-shaped 

 disks. The fronds are rigid, with a well- 

 marked midrib, green above, purple beneath. 

 It grows on moist banks, or by the side of 

 mountain streams. 



BIBL. Hook. Brit. Flor. ii. pt. 1. p. 108 ; 

 G. W. Bischoff, Nova Acta, xvii. p. 1001. 

 pi. 69. fig. 1; Endlich. Gen. Plant. No. 468. 



RED SNOW. The remarkable phseno- 

 menon known under this name has been the 

 subject of very extensive investigation, and 

 it is well known to be the result of the enor- 

 mous development of a microscopic organism 

 related to Protococcus or Chlamidococcus 

 viridis. We are inclined to believe that more 

 than one form is comprehended at present 

 under the name of Protococcus or Hcematococ- 

 cus nivalis, for our specimens of Arctic red 

 snow (for which we are indebted to the kind- 

 ness of Mr. R. Brown) appear to belong to 

 the same genus as Palmella cruenta, as first 

 indicated by Mr. Brown, and confirmed by 

 Sir W. J. Hooker. Dr. Greville's figures of 

 the Scotch plant closely resemble this ; but 

 the continental plants, described by Mr. 

 Shuttleworth and others, would seem con- 

 generic with Protococcus (Chlamidococcus, 

 Braun, Chlamidomonas,lZhr.), since they pro- 

 duce active zoospores, the forms which 

 Shuttleworth described as distinct infusoria, 

 as species of Astasia. Nearly connected 

 with this continental snow-plant, if not 

 identical, is the Protococcus pluvialis, de- 

 scribed so elaborately by Dr. Cohn, which 

 moreover appears to be synonymous with 

 the Discer&a purpurea of Morren. 



The following is a description of the red 

 snow (brought home by Capt. Parry) from 

 our own observation. It may be noticed as 

 remarkable, that after being kept so many 

 years in a moist state in a stoppered bottle, 

 the structure appears almost unchanged, the 

 only difference being the assumption of a 

 green colour on the surface of the masses 

 when exposed to light. Frond an indefinite 

 gelatinous mass densely filled with spherical 

 cells, about 1-1200" in diameter (PI. 3. fig. 

 3 d) ; cells with a distinct membrane, their 

 contents consisting of numerous tolerably 

 equal granules, red or green (see above). 

 Between the large cells lie patches of minute 

 red granules (as in Palmella cruenta, PI. 3. 

 fig. 3 a, b), apparently discharged from the 

 large cells. Bauer and Greville both de- 

 scribe this as the mode of propagation of the 

 plant, but it is probable that the cells also 



