HYDROMETRID.E. [ 403 ] 



HYDRURUS. 



2. Tliecaplwra (Sertularina, Johnst.), in 

 which the Hydroida are furnished with 

 thecae. Faui. : 



Campanulariidae. Coppiniidae. 



Campanulinidse. Haleciidae. 



Leptoscyphidae. Sertulariidae. 



Lafoeidae. Plumulariidae. 

 Trichydridae. 



3. Gymnochroa (Hydrina, Johnst.). Poly- 

 pidom absent ; locomotive. Fam. 1. Hy- 

 dridaa. 



The polypidoms of the Hydroid Polypi 

 form interesting 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, 11, 15, 16) ; and the species can be 

 identified from the polypidoms. They may 

 be mounted, after being well-washed in 

 distilled or rain-water, in balsam or gly- 

 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. Johnston, Br. Zooph. 5 ; Gosse, 

 Mar. Zool. 1, 18; Allman, Ann. N. H. 1863, 

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

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

 (Barents Sea); Mereschowski, ibid. 1878, 

 ii. 251 ; Korotneff, ibid. 1878, ii. 351 ; 

 Thompson, ib. 1879, iii. 97 ; Pascoe, Zool. 

 Class. 1880. 



HYDROMET'RID^]. 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 

 hairs, which prevent them from becoming 

 wetted. The eggs of Hydrometra are ellip- 

 tical and elegantly sculptured. 



BIBL. Westwood, Introduction, ii. 467. 



HYDROMORI'NA, Ehr. A family of 

 Infusoria. 



The two genera of which it consists, Po- 

 lytoma and Spondylomorum, appear to be 

 Monads, or species of Algae, undergoing 

 division. See these genera. 



BIBL. Ehrenb. Ber. d. Berl. Akad. 1848. 



HYDROPH'ILTJS, Geoff See HYDROUS. 



HYDROPH'ORA, Tode. A genus of 

 Mucorini (Phycomycetous Fungi). Moulds 

 growing on the dung of animals, distin- 

 guishedby the indurated persistent peridiole 

 and the conglobated spores. Two species 

 are described as British. 



H. stercorea, Tode. Fleecy ; filaments 

 simple, very long, fugacious, white ; peri- 

 dioles spherical, yellow, subsequently black. 

 Common on dung after much rain. 



If. murina, Fr. Filaments scattered, 

 short, simple, persistent, white ; peridioles 

 yellow, subsequently opaque. On rats' dung. 

 (Mucor fulvus, Sowerby, pl/400. fig. 4.) 



BIBL. Berkeley, Hook. Br. Fl. ii. pt. 2. 

 331 ; Fries, Syst. Mycol. iii. 314, Sum. Veg. 

 87. 



H YDROSE'RA, Wall. A genus of Dia- 

 tomaceae. 



Char. 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. 



H. compressa. Valves oblong. East Indies. 



H. triquetra (PI. 51. fig. 40). Valves 

 triangular. East Indies. 



H. tricoronata. New Zealand. 



BIBL. Wallich, Qu. M. J. 1858, vi. 251 ; 

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



HYDRO'US, Linn. A genus of Coleo- 

 pterous Insects, of the family Hydrophilidae. 



H. piceus 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 1|" 

 in length. The full-grown 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. 1. Insectes ; Stephens, Br. 

 Beetles. 



HYDRU'RUS, Ag. A genus of Pal- 

 me! laceae (Confer void Algae), which seems 

 to form a link between these and the UL- 

 VACE^;. The frond consists of a branched, 

 feathery, very gelatinous expansion, the 

 branches set with minute processes or ra- 

 melli (PI. 7. fig. 8) ; in the gelatinous 

 substance are imbedded minute cells with 

 homogeneous green contents, most closely 

 set in the ramelli, more scattered in the 

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

 Ducluzelii, 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. Harvey, Br. Ala. (1 ed.) 180- 

 Hassali, Alg. 302, pi. 77. fig. 3 ; Kutzin^, 

 2 D2 



