38 CCELENTERATA AND 



rooted by a creeping stolon. Hydrothecae biserial, alter- 

 nate, orifice toothed. Operculum of several pieces. 



jS. polyzonias. 



Diphasia. Plant-like. Stem branching, jointed, rooted 



by a creeping stolon. Hydrothecae opposite, pair on each 



internode. Valve-like operculum. Gonothecas scattered, 



different in male and female. 



D.fallax. 

 Sertularia (Dynamena). Plant-like; stem branching, 

 jointed, rooted by creeping stolon. Hydrothecae biserial, 

 opposite or alternate. No operculum. Gonothecse scat- 

 tered . 



S. pumila. 

 Antennularia . Plant-like. Stems simple or branching, 

 with verticillate branohlets and rooted by a mass of fibres 

 Hydrothecae cup-shaped. Nematophores bithalmic on 

 stem. 



A. spj 



Plumularia. Hydrothecae sessile, unilateral. With 



nematophores or minute cups which contain an extensile 



offshoot from the ccenosarc, with or without nematocysts. 



Gonozooids fixed. 



P. Verrillii. 

 Aglaophenia. Plumose, simple or branched, rooted. 

 Hydrothecae cup-formed. Nematophores on the Hydro- 

 thecae. Gonothecse in the form of corbulse. 



A. arborea. 



Order II. Trachymedusce. 

 Sense-bodies with a hood. With a bell-cavity and ve- 

 lum. Medusae transparent, of small size resembling in 

 many particulars the Hydroida. Body disk-like, spheri- 

 cal, conical ; colorless. Walls sometimes rigid, sometimes 

 flexible. Marginal tentacles stiff, sometimes easily decid- 



