C(ELENTERATA. 



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

 those mentioned, Eudendrium, Tubularia, and Thamnocnida; of medusae, 

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



Order IV. Campanulariae = Leptomedusae (Calyphoblastea). 



These forms are readily distinguished from the last by the fact that 

 they are always colonial and possess hydrotheeae, the medusas always being 

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

 gonothecae, closed perisarcal envelopes, inside which the gonophores arise 

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

 (fig. 174, /). The typical Campanulariae produce medusae, while some 

 forms, like Thaumantia * and JEquoria * have no hydroid stage, and 

 on the other hand Sertularia * and Plumularia * have no medusa stage. 



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

 Calycellasyringa; C, Obelia dichotoma ,' Z>, Opercularella pumila. 



Other common genera, Clytia,* Dipliasia* and Aglaophetiia* among 

 hydroids; Obelia,* Tima* RUegmatodes* among medusae. Possibly the 

 fossil group of GRAPTOLITES belongs near here. Only the perisarc is 

 known, and this is composed of hydrothecae, in which it is supposed the 

 hydranths occurred. 



Order V. Trachymedusae. 



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

 characters are given on p. 239, Trachynema, Liriope*(ftg. 183), and Cam- 

 panella in our own waters, Geryonia, etc., in Europe. 



Order VI. Narcomedusae. 



In addition to the characters on p. 239 may be added the fact that the 

 tentacles arise from the outside above the rim of the bell. Cunocantha * 

 (fig. 183), and Cunina * in our warmer waters, jEgina in Europe. 



