KHOPALONEMA VELATUM. 129 



mens of the " Plankton " expedition described by Maas ('93) under the name 

 B. striatum. Could this be shown to be the case, the name R. striatum should 

 be substituted for R. fwierarium. 



It is probable that all of the species referable to Rhopalonema which 

 have yet been described belong to either one or other of these two species. 

 So many of the names, e. g. all those referred by Haeckel to Marmema, 

 and the majority of those referred by him to Trachynema, were based 

 on larval stages or on poorly preserved material that the synonymy of the 

 species is difficult. The size and habitat of most of the described forms, 

 however, make it almost certain that they fall under R. velatutn. 



I have been able to satisfy myself by an examination of specimens that 

 this is likewise true of R. typicum Agassiz and Mayer (: 02), supposed by 

 them to be identical with Homoeonema typicum Maas ('97), which, however, 

 belongs to a different genus ; and also of the specimens from the Mal- 

 dive Islands, which I recorded under the same name (: 04, p. 256). The 

 case of R. typicum, Hargitt (: 02) from the Gulf Stream must remain doubt- 

 ful, since Hargitt states (: 05^ p. 54) that it has numerous cirri between the 

 radial tentacles, a character showing that it certainly is not related to Maas's 

 H. typicum. 



Rhopalonema velatum Gegenbaur. 



Rhopalonema velatum Gegenbaur, '56, p. 251, taf. 9, figs. 1-5 ; Haeckel '79, p. 264 ; 



Vanhoffen, : 02b, p. 59^ taf. 10, figs. 16, 28, taf. 11, fig. S2. 

 Rhopalonema coeruleum Haeckel, '79, p. 264, taf. 17, figs. S-6 ; Browne, : 06, p. 172 



{non Maas, : 05). 

 Rhopalonema polydactylum Haeckel, '79, p. 265, taf. 17, figs. 7-11. 

 Rhopalonema typicum Agassiz and Mayer, : 02, p. 152, pi. 5, figs. 21, 22 ; Bigelow, : 04, 



p. 256. 



The following are undoubtedly young stages of this species : — 



Trachynema octonarium Haeckel, '79, p. 260. 



Sminthea tympanum (et globosa) Gegenbaur, '56, p. 246, taf. 9, figs. 17, 18. 

 Marmema tympanum Haeckel, '79, p. 262. 

 Sminthea globosa Keferstein und Ehlers, '61, p. 89. 

 Marmema clavigerum Haeckel, '79, p. 263, taf. 17, figs. 1, 2. 

 Calyptra umbllicata Leuckart, '56, p. 14, taf. 1, figs. 9, 10. 

 Rhopalonema umbilicatum L. Agassiz, '62, p. 366. 

 Marmema umbilicatum Haeckel, '79, p. 263. 

 Marmema velatoidea Maas, '93, p. 13, taf. 1, fig. 6. 



9 



