HALACARUS. 



[ 381 ] 



IIALIONYX. 



scandens, the spiral-fibrous hairs take rather 

 the form of miiurte scales, ami they do not 

 spontaneously expand elastically (Pi. 28. 

 fig. 20). Among the Ooniposit;c, these 

 spiral-fibrous hairs have been observed on 

 the pericarp of Huckeiia, some species of 

 'TrichocUne, Eiiriops, 31eso(/rainma, Doria 

 Clmfticefolia, OUyothrix gracilis, and some 

 species of Senecio. Spiral cells also occur 

 on the seed of JL/drocharis. The best way 

 to observe the elastically expanding hairs is 

 to place a thin slice of the skin of the seed 

 on a slide in a little alcohol, which does not 

 sot'ten the cell-wall : when the object is in 

 focus, the addition of a little water causes 

 the gelatinous softening of the cell-walls, 

 the spiral hbres fly out from the surface of 

 the seed-coat and show clearly the charac- 

 ter of these beautiful objects. The primary 

 membrane may be detected, even in its 

 gelatinous state, by adding sulphuric acid 

 and iodine, which produce a purplish or 

 violet colour. Further remarks on this head 

 will be found under Spirai, Stkuctuhes. 



The hairs on the stigma of Campamda 

 are remarkable for the intussusception which 

 is observed to take place in the mature hairs. 

 The filiform processes growing from the 

 under siu-face of the frondose HepaticjB, 

 the thallus of Lichens, the prothallium of 

 Ferns, kc, are commonly called radical 

 hairs. In most cases they present no re- 

 markable points of structure ; in Marchan- 

 tia, however, peculiar spiral markings have 

 been detected (see Marchantia). 



BiBL. Meyen, Secretions-oryane d. Pflan- 

 zen, 1837 ; id. P/ianzen-jjhysiol. ; Cohn, Cu- 

 ticida, Linncea, xxiii. 3o7, 18o0 ; Schleiden, 

 Midler'' s Arc/iiv, 1838; Beitr. z. Botanik, 

 Leipsic, 1844, i. 121 {Sc. Memoirs) ; De- 



caisne, Ann. Sc. 



Nat. 2 ser. xii, 

 X. H. vi. 257 ; 



251, pi. 4 ; 

 Brongniart, 

 pi. 4; Pril- 



5; Tuiien 

 Weisse, I>. 



Leighton, Ann. 



Ann. Sc. Nat. 2 s^r. xii. 244, 

 lieux, Ann. Sc. Nat. 4 ser. -^ 

 West, Qu. Mic. Jn. vii. 22; 

 Pflanzenhnare, 18G7 ; Hanstein, Bot. Zeit. 

 1868, 6U7 ; Banter, Trichomgeh. 1871; 

 Martinet, Ann. Sc. Nat. 1872, xiv. ; Sachs, 

 Bot. 103. 



HALACARUS, Gosse.— A genus of 

 marine Acarina. 



Char. Body sometimes covered with a 

 dorsal shield ; rostrum bulbous, pointed ; 

 palpi terminated by a fang-like claw; legs 

 formed f()r walking, arising from the outer 

 margin of the body, directed two pairs for- 

 wards and two backwards, and with a pair 

 of hooks. 



Five species : found crawling upon sea- 

 weeds at low water, or in dredgings. 



BiBL. Gosse, 3far. Zool. i. 177 ; Murray, 

 Econ. Entoin. 205 (tigs.). 



IIALAKACH'NE, AUman.— A genus of 

 marine Acarina ; family Gamasea. 



Body elongate subcyliudrical, with an 

 anterior dorsal plate, 



//. halichceri. In the posterior nares of a 

 seal (Ilalicharus grgphus) ; length 1-8". 



BiBL. Aliman, Ami. N. II. 1847, xx. 

 47 ; Murray, Econ. Ent. 167 (tigs.). 



HALECTID.E, Hincks.— A family of 

 Ilydroid Zoophytes. 



Gen. : Huleciuni and OpModes. 



HALE'CIUxM, Oken.— A genus of Hy- 

 droid Zoophytes, family Sertukriid;e. 



Distinguished by tlie plant-like polypi- 

 dom, the stem consisting of numerous 

 parallel capillary tubes, and the cup-like 

 nearly sessile cells arising alternately on 

 opposite sides of the stem, one under each 

 joint. 



H, hulecinmn. Vesicles oval or oblono-. 

 Common on shells and stones in deep water ; 

 4-10" high. 



H. Bcanii. Vesicles calceohform. Rare. 



H. muricatum. Vesicles spinous. 



5 other species. 



BiBL. Johnston, 5/7^. Zooph.oS: Hincks, 

 Ilydroid Zooph. 220. 



HALIOHOND'RIA, Flem.— A genus of 

 Sponges. 



HALTDRYS, Lyngb.— A genus of Fu- 

 cacese (Fucoid Algas), containing one British 

 species, H. siliquosa, common on rocks and 

 stones somewhat above low-water mark. 

 It is readily distinguished by its pod-like 

 septate air-vessels. The fructification, which 

 is terminal on the branches, much resembles 

 that of Fucus, except that the interior 

 of the receptacles is tilled up with hrni 

 polygonal cellular tissue. The antheridia, 

 moreover, are terminal on their pedicels, 

 often in tufts, short in form, and inter- 

 mixed with spore-sacs in the same concep- 

 tacle. 



BiBL. Harvey,-^;-. Mar. Alg. 15, pi. 1 C ; 

 Thuret, Ann. Sc. Nat. 3 ser, xvi. 8, pi. 3. 



HALIO'N YX, Ehr.— A genus of Diato- 

 macese. 



_ Char. Frustules single; valves equal, 

 circular, surface radiate, the rays not com- 

 mencing at the umbihcu.-i; no internal septa. 

 Marine. 



//. senarius. Rays six, the intervenino- 

 spaces with shorter rays of equal len^-th 

 parallel to the larger, and with transverse 



