TRACHYMEDUS^E — RHOPALONEMA. 



377 



The marginal lithocysts, however, increase with age, and when young the medusae have but 

 4, then 8, and, finally, 1 6 or more. Moreover, they are very irregular and variable in their 

 development and are readily lost, and I have seen medusas in which one octant exhibited the 

 characters of "Rhopalonema" while the other 7 octants remained in the"Trachynema" stage. 



Maas, 1893, 1897, 1904, and 1905, restricts Rhopalonema to include medusas with two 

 different sorts of marginal tentacles, as we have defined them. In contrast to this he introduces 

 a new genus, Homceonema, to include medusas with tentacles all alike, but bearing no definite 

 numerical relation to the radial-canals. Both of these genera have the 8 gonads restricted to 

 definite, limited portions of the 8 radial-canals; and Maas defines another genus, Pantachogon, 

 to include medusas with gonads diffusely developed upon the entire lengths of the radial-canals, 

 while in Rhopalonema and Homceonema they are localized. I define Rhopalonema in the sense 

 proposed by Vanhoffen, 1902. 



Tabular Synopsis of the Species of Rhopalonema. 





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