BRITISH ZOOPHYTES. 35 



The Hydroida have been divided by Mi\ Hincks 

 into three sub-orders : 1 . The Athecata ; 2, the 

 Thecaphora, and 3, the Gymnochroa. These sub- 

 orders exactly correspond with those established by 

 Prof. Allman, and which, he names Gymnohlastea, 

 Calijptohiastea, and Eleutherohlastea. 



The sub-order Athecata, or Gymnoblastea, contains 

 those genera in which the polyps and gonophores are 

 not lodged in external protective receptacles, that is, 

 are not protected by hydrotliec^ or gonothecee. This 

 sub-order contains the families Olavidce, Hydractiniidce, 

 Podocorynidce, Hydrolaridce, Corynidce, Pennariidoe, 

 GlavateUidce, MyriothelUdce, Eudendriidcs, BimeridcB, 

 and Tubulandce. The characteristics of these families 

 are based upon the shape of the hydranths or poly- 

 pites, and the disposition of tbe tentacles. Prof. 

 Allman introduces the method of reproduction into 

 his family characteristics, but I have thought it 

 advisable so far as possible to retain Mr. Hincks' 

 divisions as having characters more easily perceptible 

 to a student. I have introduced into the text or foot- 

 notes references to Prof AUman^s families and genera 

 wherever they diifer from those of Mr. Hincks. 



In the sub-order Thecaphora, or Calyptohlastea, the 

 zooids are protected by thecge. This order contains 

 the Oamjoanidariida, Camj^anulinidw, Lej^toscyj^hidce, 

 Lafoeidce, Trichydridce, Copjjiniida, Haleciidce, Sertu- 

 lariidce, and Plumulariidce. 



The sub-order Gymnochroa, or Eleutherohlastea, 

 contains the single family Hydrida, in which the polyp 

 is destitute of a polypary and is locomotive. This 

 family comprises one genus hydra. 



The only fresh- water hydroids are Cordylophora 

 lacustris and the various species of Hydrve. 



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