HORNBLENDE. 



[ 396 ] 



HYDATIN^A, 



also forms an interesting object of the same 

 kind. 



BiBL. Bonders, Mulder^s Phys. Chem. ; 

 Owen, Brande's Diet., art. Cornua. 



HORNBLENDE. See Rocks. 



HOR'NEUA, Lam.— A genus of Cyclo- 

 stoniatons Polyzoa, 2 species. (Hiucks, 

 Poh/zoa, 407.) 



HORSE-LEECH. See H^mopis. 



HUXLEY'A, CI. & Lachm.— Agenus of 

 Hypotriclious Infusoria, of the family Er- 

 TJlina. T\\'o species : 



//. snlcafa. Jiody greatly compressed ; 

 cuticle with oblique furrows. Bergen. 



II. crassa. Body scarcely compi'cssed, 

 almost as thick as broad, thickest bt'hind ; 

 cuticle smooth ; length 1-1250". Bergen. 



BiBL. Clap. & Lachmann, Inf. 290. 



HUXLP]Y'A,Dyster. — A genus of Chei- 

 lostomatous Polvzoa. H. frayilis, Tenby. 

 (Hincks, Pohr.. 2d.) 



HYALODIS'CUS, Ehr. = Cyclotella, 

 Kiitz. in part. 



H. Iccvis = CycloteMa Icevis ; Il.-patagonica 

 = Cyl. pat agon. ; H. suhtilis, Bail., with 

 extremely tine dots, is used as a test-object. 



BiBL. Ehreubcrg, Perl. Per. 1845, 78 & 

 155 ; Kiitzino-, Sp. Alq. 20. 



HYALOM'MA, Koch.— A genus of 

 Ixodes, (Acarina), wdth the eyes clear, dis- 

 tinct and conical. Three or four species, 

 occurring in the Caucasus and Spain. 

 (Koch, Uehers. ; Murray, Ec. Ent, 196, 

 figs.) 



ITYALOP'TERUS, Koch.— A genus of 

 AphidfE. DilFering from Aplns chiefly in 

 the shortness of the tail and nectaries, and 

 the oval, often linear form of the body. Six 

 species : found on the plum, the reed, the 

 moss-rose, the columbine, iiilene injjata, 

 and Eriophorum, (Buckton, Aphides, Pay 

 Soc. ii. lOi).) 



HYALOSI'RA, Kiitz.— A genus of Dia- 



tomacea3. 



Char. Frustules compound, rectangular, 

 tabular ; with alternate vitta;, interrupted 

 in the middle, and connected with those of 

 the opposite side by fine lines ; loAvcrmost 

 frustule attached by a stipes which is affixed 

 to one angle. Marine. 



The fine lines at the end of the vittte 

 give the latter a forked appearance. The 

 frustules are often partly separated, so as to 

 be connected with each other by one angle 



only- p ^ 



Four species, probably forms of Tetracy- 



cliis. . 



II. rectamjula (PI. 17. fig. 1). Stipes 



short, fi'ustules subconcatenate, in front view 

 subquadrate ; rectangular ; length 1-1360". 



BiBL. Kiitzing, Pacillar. 125 ; Sp. Alg. 

 115 ; Rabenhorst, Fl. Ah;, i. 306. 



HYALOSPIIE'NIA.— A genus of Rhi- 

 zopoda (Bronn, Klass. kc, pi. i. fig. 18). 



HYALOTHE'CA, Ehr.— A genus of 

 Desmidiaceae. 



Char. Cells united into an elongated, 

 cylindrical filament, which is surrounded 

 by a gelatinous sheath ; cells in front view 

 slightly constricted, so as to give the margins 

 a crenate appearance ; or having a grooved 

 rim surrounding one end, and forming a 

 bidentate projection ; end -slew orbicular. 



The filaments are not twisted, and are 

 always of the same apparent breadth. Spo- 

 rangia orbicular, smooth. 



H. dissiliens (PI. 14. fig. 1, front view of 

 filament; 2, end view). Filament fragile, 

 margins crenate ; breadth of filament 1-1300 

 to 1-800". The transparent sheath of this 

 beautiful object is so delicate as to be easily 

 overlooked. Sporangia (fig. 314) situated 

 within the connecting tube. 



Not uncommon in clear boggy pools. 



II. mucosa. Filament scarcely fragile ; 

 joints not constricted, surrounded at one 

 end by a miimte furrowed rim, forming in 

 the front view a bidentate projection ; 

 breadth of filament 1-1250 to 1-1100". 



The fm-rowed rim of each cell is on the 

 same side as that of the contiguous cell. 



BiBL. Ralfs, Brit. Desmid. p. 51. 



HYDATl'NA, Ehr.— A genus of Rota- 

 toria, of the family Ilydatinsea. 



Char. Eyes absent ; jaws two, teeth nu- 

 merous, free ; foot forked. 



H. sevta (PI. 43. fig. 37 ; fig. 38, teeth). 

 Body conical, hyaline ; margin of rotatory 

 organ ciliated ; foot robust ; aquatic ; length 

 1-48 to 1-30". . 



This animal forms a favourable subject 

 for the examination of the typical structure 

 of the Rotatoria, and is that which Ehren- 

 berff used as the basis of his investigations 

 upon tlieir organization. 



II. brachydacti/Ia. Segments of foot 

 short ; body suddenly narrowed at the base 

 of the foot; aquatic; length 1-144". 



BiBL. Ehrenberg, Infus. 412 ; Colin, 

 Sieh. Si' Koll Zeitschr. vii'. 



HYDATIN^'A.— A family of Rota- 

 toria. 



Char. Neither carapace nor enveloping 

 sheath present ; rotatory organ multiple, or 

 more than bipartite. 



18 genera. 



