114 HYDrtOZOA. 



Family 5. Ehizophtsiadjs. 



Fneumatocyst small. Coenosarc filiform. 

 Nectocalyces and hydrophyllia absent. 

 Tentacida having branches, without sac- 

 culi. 



Family 6. PHTSALiADiE. 



Fneumatocyst occupying almost the whole 

 of the thick and irregularly fusiform ccenosarc. 



Nectocalyces and hydrophyllia absent. 



Tentacula with basal sacs, but no lateral 

 branches. / 



Family 7. Velellio^. 



Fneivmatocyst flattened, divided into cham- 

 bers by numerous concentric partitions, and 

 occupying almost the whole of the discoidal 

 ccenosarc. 



Nectocalyces and hydrophyllia absent. 



Tentacula short, clavate, simple or branched, 

 submarginate. 



A single central, principal polypite. 



7. Order 6: Medusidae. — If the phyogem- 

 maria of Velella and Forpita be regarded as 

 gonoblastidia, the hydrosoma of these genera may 

 then be said to present not more than one true 

 polypite ; a character in which they differ from 

 all other Fhysophoridce, but agree with the mem- 

 bers of the next order, Medusidce. Cuvier, in- 

 deed, associated the Velellidce, Medusidcc, and 

 free zooids of the Lucernaridce in a single group, 

 under the name of " Acalephes Simples " ; the re- 

 maining Fhysophoridce, together with the Caly- 

 cophoridcCf being distinguished as " Acalephes 

 Hydrostatiques ". But the Velellidce, like all other 



