HYALOTHECA. 



[ 327 



HYALOTHECA, Ehr.— A genus of Des- 

 tnidiacese. 



Char. Cells united into an elongated, cy- 

 lindi-ical filament, which is surrounded by a 

 gelatinous sheath ; cells in front view slightly 

 constricted, so as to give the margins a cre- 

 nate appearance ; or having a grooved rim 

 surrounding one end, and forming a biden- 

 tate projection; end \\q\\ orbicular. 



The filaments are not twisted, and are 

 always of the same apparent breadth. Spo- 

 rangia orbicular, smooth. 



H. dissiliens (PI. 10. 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 (figs. 3, 4) situated 

 within the connecting tube. 



Not uncommon in clear boggy pools. 



H. mucosa. Filament scarcely fragile; 

 joints not constricted, surrounded at one end 

 by a minute furrowed rim, forming in the 

 front view a bidentate projection ; breadth 

 of filament 1-1250 to 1-1100". 



The furrowed rim of each cell is on the 

 same side as that of the contiguous cell. 



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



HYDATINA,Ehr. — A genus of Rotatoria, 

 of the family Hydatinsea. 



Char. Eyes absent ; jaws two, teeth nu- 

 merous, free; foot forked. 



H. senta (PI. 34. fig. 37 ; fig. 38, teeth). 

 Body conical, hyahne ; margin of rotatory 

 organ ciliated ; foot robust; aquatic; length 

 1-48 to 1-36". 



This animal forms a favourable subject 

 for the examination of the typical struc- 

 ture of the Rotatoria; and is that which 

 Ehrenberg used as the basis of his investiga- 

 tions upon their organization. 



H. brachydactyla. Segments of foot short ; 

 body suddenly narrowed at the base of the 

 foot; aquatic; length 1-144". 



BiBL, Ehrenberg, Infus. p. 412. 



HYDATIN^A.— A family of Rotatoria. 



Char. Neither carapace nor enveloping 

 sheath present ; rotatory organ multiple, or 

 more than bipartite. 



18 genera. 



Eyes absent. 



No teeth Enteroplea. 



Teeth present. 



Jaws with numerous teeth Hydatina. 



„ with a single tooth Pleurotrocha. 



Eyes present. 

 Eye single. 

 Eye frontal. . 

 ,, cervical. 



Furcularia. 



] HYDRA. 



Foot styliforra Monocerca. 



„ forked. 



Frontal cilia, no hooks norstyles Notommuta. 

 „ styles present . . Si/nchata, 



„ hooks Scaridium. 



Foot absent ] with cirrhi or fins. , Polyarthra. 



Eyes two. 

 Eyes frontal. 



Foot forked Diglena. 



„ styliform. 



With cirrhi Triarthra. 



Without cirrhi Rattuliis. 



Eyes cervical Distemma, 



Eyes three. 

 Eyes not stalked. 



Eyes cervical Triophthalmus. 



Two eyes frontal, one cervical . . Eosphora. 

 Two frontal eyes stalked, one cervi- 

 cal not stalked Otoglena. 



Eyes more than three in a single group Cycloglena. 

 >> ,, two groups. . Theorus. 



BiBL. Ehrenberg, hfus. p. 410. 



HYDNEI. — A family of Hymenomyce- 

 tous Fungi, characterized by bearing their 

 basidiospores on tubercles or spine-hke pro- 

 cesses on the under side of a discoid, cup- 

 shaped or funnel-shaped, stalked or sessile 

 pileus. The basidiospores are seen by making 

 cross sections of the spines, &c. See Basi- 

 diospores, Hymenomycetes. 



BiBL. Berkeley, On the Fruct. of Hyme- 

 nomycetous Fungi, Ann. Nat. Hist. i. 81 ; 

 Leveille, Sur VHymenium des Champignons, 

 Ann. des Sc. nat. 2 ser. viii. 32. 



HYDRA, Linn. (Freshwater Polype).— 

 A genus of Polypi, of the order Anthozoa 

 and family Hydrina. 



Char. "Locomotive, single, naked, gelati- 

 nous, subcyhndrical, but very contractile and 

 variable in form ; the mouth surrounded by 

 a single row of filiform tentacles. Propaga- 

 tion by the formation of gemmae and ova 

 upon or within the substance of the body 

 of the animal. 



1. Hydra viridis (PI. 33. fig. 21, adhering 

 to the radicles of duck-weed {Lemna) ), Body 

 leaf-green, cylindiical or insensibly narrowed 

 towards the base; tentacles 6 to 10, shorter 

 than the body. 



Common in ponds and still waters. Ten- 

 tacles narrowest at their origin. 



2. H. vulgaris. Body orange-brown, yel- 

 lowish or red, cylindi-ical ; tentacles 7 to 12, 

 as long as or longer than the body. 



Tentacles tapering to the free ends. 

 Found in weedy ponds and slowly running 

 waters. 



3. H. attenuata. Body pale olive-green, 

 attenuated below; tentacles pale, longer 

 than the body. 



In ponds ; rare. 



4. H. fusca. Body brown or greyish 



