IlYDKOMETrvID.E. [ 403 ] 



HYDRURUS. 



2. Thecaphom (Sertularina, Johnst.), in 

 ■wliich the Ilydroida are furuished with 

 thocae. Faiu. : 



Campamiliiviidre. 



Campaniiliiiid;i3. 



Leptoscyphidse. 



liafoeidiB. 



Trichvdridte. 



Coppiniid.*B. 

 Haleciida\ 

 Sertulariidic. 

 Phimulariida3. 



3. Gi/mnochroa (Ilydrina, Johnst.). Poly- 

 pidom* absent; locomotive. Fain. 1. Hy- 

 diidfB. 



The polypidoms of the Ilydroid Polypi 

 form interest iiiij microscopic objects. They 

 are very common among sea-weeds, on 

 shells, rocks, &c., the forms being often 

 elegantly branched and feathery (PI. 41. 

 figs. 4, il, lo, 1()) ; and the species can be 

 identified from the polypidoms. They may 

 be monnted, after being well-washed in 

 distilled or rain-water, in balsam or glj^- 

 cerine. The animals are very irritable and 

 contractile, and can only be observed after 

 the removal of the bodies to which they are 

 attached to an aquarium or jar containing 

 sea-water. 



BiBL. Joliuston, Br. Zoopk. 5 ; Gosse, 

 Mar. Zool. 1, 18 ; Allmau, Ann. N. II. 18G3, 

 xi. 1 ; Hincks, Br. Zooph. i ; and Ann. N. H. 

 1877, xix. 148, 1878, i. 239 ; 1880, vi. 277 

 (Barenfs Sea) ; Mereschowski, ibid. 1878, 

 ii. 251 ; Korotneft", ibid. 1878, ii. 351 ; 

 Thompson, ih. 1870, iii. 97 ; Pascoe, Zool. 

 Class. 1880. 



HYDROMET'RID.F;.— A family of He- 

 mipterous (Heteropterous) Insects, the spe- 

 cies of which are found skimming the sur- 

 face of pools or rivers. The under parts of 

 the body and legs are covered with fine 

 hau-s, which prevent them from becoming 

 wetted. The eggs of Ilydrometra are ellip- 

 tical and elegantly sculptured. 



BiBL. Westwood, Infroditction, ii. 407. 



HYDROMOKI'NA, Ehr.— A family of 

 Infusoria. 



The two genera of which it consists, Po- 

 lytoma and Spondyhimorum, appear to be 

 Monads, or species of Algaj, undergoing 

 division. See these genera. 



BiBL. Ehrenb. Ber. d. Berl. Akad. 1848. 



H Y1)R( )PH 'ILUS, Geoff'. See IlYDEOf s. 



HYDR()PH'ORA, Tode.— A genus of 

 Mucorini (Pliycomycetous Fungi). 3Ioulds 

 growing on the dung of animals, distin- 

 guished by the indurated persistent peridiole 

 and the conglobated spores. Two species 

 are described as British. 



H. stereorea, Tode. Fleecy ; filaments 

 simple, very long, fugacious, white; peri- 

 dioles spherical, yellow, subsequently black. 

 Common on dung after much rain, 



H. mnrina, Fr. Filaments scattered, 

 short, simple, persistent, white ; peridiolus 

 yellow, subsequently opaque. On rats' dung. 

 i^Mucor fulviis, Sowerbv, pi.' 400. fig. 4.) 



BiBL.' Berkeley, Hook. Br. Fl. ii. pt. 2. 

 331 ; Fries, Syst Glycol, iii. 314, Smn. Fey. 

 87. 



IIYDROSE'RA, Wall.— A genus of Dia- 

 tomacete. 



C7iar. Frustules quadrate, areolar, united 

 into a filament, with internal septa ; hoop 

 smooth, compressed or triangular in front 

 view, areolar, the constricted angles with a 

 small appendage on one side. Marine. 



//. compressa. Valves oblong. East Ind'es. 



//. triquef.ra (PL 51. fig. 40). Valves 

 triangular. East Indies. 



H. tricoronata. New Zealand. 



BiBL. Wallich, Qii. M. J. 1858, vi. 251 ; 

 Stolterforth, Jn. Mic. Soc. 1881, 424. 



HYDRO'tJS, Linn.— A genus of Coleo- 

 ptei'ous Insects, of the family Hydrophilidfe. 



H. picens is one of the largest aquatic 

 British beetles. We have selected the head 

 to illustrate the structure and arrangement 

 of the trophi, &c. in the Coleoptera (see 

 Insects). The perfect insect is about I5" 

 in length. The fuU-groAvn larva is about 3" 

 long; it has no lateral branchiae, but two 

 filiform branchial appendages at the end of 

 the body. 



BiBL. Westwood, Introduc. ; Dumeril, 

 Consid. gen. s. I. Insectes ; Stephens, Br. 

 Beetles. 



HYDRU'RUS, Ag.— A genus of Pal- 

 mellaceaj (Confervoid Algfe), which seems 

 to form a link between these and the Ul- 

 VACE.'E. The frond consists of a branched, 

 feathery, very gelatinous expansion, the 

 branches set with minute processes or ra^ 

 melli (PI. 7. fig. Sa) ; in the gelatinous 

 substance are imbedded minute cells AA-ith 

 homogeneous green contents, most closely 

 set in the ramelli, more scattered in the 

 older part of the frond (PI. 7. fig. 8b). II. 

 Di<cliizelii, Ag., grows to a length of from 

 1 to 6", and from 2 to 4'" in diameter, 

 attached to stones in •mountain-brooks and 

 rivers ; the recent frond is of brownish 

 olive in mass, green when dried. When 

 fresh it has a very offensive smell. Repro- 

 duction by active gonidia. 



BiBL. iTarvev, Br. Ah/. (1 ed.) 180; 

 Hassall, ^%. 302, pi. 77. "fig. 3; Kiitziug, 



2d2 



