126 



HYDROZOA 



Not far from Pelagia, but in a family by itself 

 Gregenbaur has placed the genus Charybdea. 



Miiller 



allied Tamoya, a distinct veil is certainly present 

 while Charybdea itself is furnished with marginal 

 processes, which seem to represent the same^ap- 

 paratus. 



Section IV. 



DISTRIBUTION OF HYDROZOA. 



I. Relations to Physical Elements. — 2. Bathymetrical Distribution. 



— 3. Geographical Distribution. 



I. Relations to Physical Elements 



The 



Hydrozoa, as a class, are almost exclusively marine; 

 Hydra and Cordylophora being the only fresh- 

 water genera hitherto described. 



2. Bathymetrical 



The ma- 



rine Hydrozoa, with reference to their dk , 



may conveniently be divided into two groups, the 

 fixed and the oceanic. The fixed Hydrozoa, Cory- 

 nidce and Sertularidce, are less abundant between 

 tide marks than at depths of a few fathoms, some 

 forms extending their range to very deep water. 

 The Corynidce are, perhaps, on the whole, more 

 partial to shallow waters than the Sertularidce, 

 certain species of the latter order, especially of the 

 genus Campanularia, being found at considerable 

 depths. But the vertical distribution of several 

 forms is more limited than that of others. Thus 

 Clava and Coryne appear usually not to wander 



