242 



CWLKNTKRArA. 



Other common genera in American waters are, of hydroids, besides 

 those mentioned, Jiudendriutn, Tnhularia, and Thamnocnida; of medusie, 

 Tiaris, Turritopsis, Dipurena, Lizzia, Noiwpsis, and Hydrichthis. 



Order IV. Campanulariffi = Leptomedusae (Calyphoblastea). 



These forms are readilj' distinguished from the last by the fact that 

 they are always colonial and possess hydrothecce, the meduste always being 

 Leptomedusae (p. 239). A peculiarity of the group is the existence of 

 gonothecse, closed perisarcal envelopes, inside which the gonophores arise 

 from the blastostyle, a specialized polyp, without moutli or tentacles 

 (fig. 174, /■). The typical Campanularia? produce medusae, while some 

 forms, like Thaumantia* iViid jEquoria* liave no hydroid stage, and 

 on the other hand Sertidaria * and Pluinulariu * have no medusa stage. 



Fig. 



186.— American Campanularians. (After Verrill.) A. Clytia noliformis ; B, 

 CaUjceJla syriufjii ; C, Olwlia dtchotonta ; />, OpercuJareUa pumila. 



Other common genera, Clytia * Dijjhusia* and Aglaoplienia* among 

 hydroids ; Ohelia* I'ima,* lihegmatodes* Among meduate. Possibly the 

 fossil group of GR.4PT0LITES belongs near here. Only the perisarc is 

 known, and this is composed of hydrolheca', in wliicli it is supposed the 

 hydranths occurred. 



Order V. Trachymedusae. 



These medusas, mostly from warmer seas, have no hydroid stage. The 

 characters are given on p. 239, Tnirhi/)ii'iii(i, Li riope* {fig. 183), and Cam- 

 panella in our own waters, Geri/ouia, etc.. iu Europe. 



Order VI. Narcomedusae. 

 In addition to the characters on ]>. 239 may lie added the fact that the 

 tentacles arise from the outside aliove the rim of tlie bell. Ciniomntha * 

 (tig. 183), and Cunina * iu our warmer waters, ^Egina in Europe. 



