HYDROZOA 117 
Order TRACHYLINE 
(No fixed zophyte stage ; always free-swimming meduse) 
Suborders Genera and Species 
TRACHYMEDUSE 
(Tentacles spring from 
margin of umbrella; a 
manubritim: longs go- Trachynema digitale 
nads in connection with 
radial canals) 
NARCOMEDUSZE 
(Tentacles spring from 
midway between sum- 
mit and margin of 
umbrella; manubrium 
short; gonads in con- 
nection with manu- 
brium) 
Order HYDROCORALLINA 
(Skeleton of carbonate of lime) 
Millepora alcicornis 
Order SIPHONOPHORA 
(Pelagic free-swimming colonies ; exhibit extreme polymorphism of zo0ids) 
Nanomia cara 
Physalia arethusa 
Vellela limbosa 
