Suborders 

 TRACHYMEDUSJE 

 (Tentacles fjiring from 

 margin of umbrella; 

 manubrium long, go- 

 nads in connection with 

 radial canals) 



NARCOMEDUS.E 

 (Tentacles spring from 

 midway between sum- 

 mit and margin of 

 umbrella ; manubrium 

 short ,- gonads in con- 

 nection with manu- 

 brium ) 



HYDROZOA 



Order TRACHYLIN.S; 



(No fixed zoophyte stage ,- always free-swimming medusas) 



Genera and Species 



117 



Trachynema digitate 



Order HYDROCOBALLINA 



(Skeleton of carbonate of lime) 



Millepora alcicornis 



Order SIPHONOPHOEA 



(Pelagic free-swimming colonies ; exhibit extreme polymorphism of zooids 



Nanomia caret 

 Physalia arethusa 

 Vettela limbosa 



