12 M. F. Miiller qu the Systematic Position of the Charybdeidse. 



to one or the other. Amongst these are jEgina citrea, which 

 approaches the higher forms in the four arms and the great 

 mobiUty of the tentacles, and jEginopsis Laurentii, which allies 

 itself to them by the four ai;ms at the mouth. So also Charybdea 

 pe?'iphyUa, Peron, which resembles Tamoya quadrumana in the 

 form of the marginal appendages, but departs from the other 

 Charybdeida in the multiplicity of its tentacles. 



I would consequently arrange the Charybdeidce in the follow- 

 ing manner in the system of the Hydromedusse ; — 



HYDROMEDUSiE. 



1. SiPHONOPHORA, including the free sexual animals {Chryso- 



mitrd), 



2. Hydroida. 



a. TubularincBi together with the Hydroid Medusae without 



organs of sense or with eye-spots. 



b. Sertularince, with the Hydroid Medusae with marginal vesi- 



cles*. 

 In respect of the development, there are in this group — 

 a. Polypes without free sexual animals. 

 /3. Polypes with free sexual animals, 

 y. Free sexual animals without polypes {Trachynema, 

 Liriope). 



3. AcALEPH^, R. Leuckt. {Discophorce phanerocarpcBy Esch.). 



a. Monostomatous (Medusidce, Esch.). 



b. Polystomatous {Rhizostomidce, Esch.). 



4. uEginoid^ (jEffincBj Liitk.). 



a. Lower : Cunina (with JEgina rosea, Esch.), Mgineta, Po- 



lyxenia, JEginopsis bitentaculata, 



b. Higher : Charybdeidce. JEginopsis Laurentii ?, jfEgina (ci- 



trea), Charybdea (marsupialis), Tamoya, Periphylla (C 

 periphylla, Vir.), 



* Gegenbaur was the first, as far as I know, who pointed out the im- 

 portance of the ocelli and marginal vesicles in the Hydroid Medusae, and 

 laid some stress upon the difference of the marginal filaments ; and, indeed, 

 the families of " Cra^edota '* established by him, from being more natural 

 and depending less upon the exclusive application of one character, con- 

 trast very advantageously with those of Forbes, and even of Liitken, and 

 may serve as a more convenient starting-point for further systematic at- 

 tempts. To future workers I would especially recommend a careful con- 

 sideration of the marginal filaments, by which, apparentl}'^, amongst other 

 things, the Geryonidce and Thaumantiadce of Gegenbaur might be more 

 sharply defined. 



