30 THE VOYAGE OF H.M.S. CHALLENGER. 



Here, as in Schkotricha iinifurcata, the first bifurcation takes place in the second seg- 

 ment of the hydrocladium, this segment carrying a bydrotheca without nematophores in 

 the angle of the bifurcation, and being preceded by a very short segment destitute of 

 hydrotheca. 



Dredged at Station 151, February 7, 1874, off Heard Island; depth, 75 fathoms; 



bottom, mud. 



Polyplumaria, G. 0. Sars. 



Polyplumaria, G. 0. Sars, Forliandl. Vidensk. Selsk. i. Christiania, 1873. 

 Diplopterun, Allman, Trans. Zool. Soc. Lond., 1873. 



Generic Character. Troj^hosome. — Hydrocladia each with an accessory hydrotheca, 

 bearing ramulus, which springs from its proximal internode. 



Gonosome. — Gonangia borne by the basal segment of the primary pinnse. 



In a report on the Hydroids collected during the expeditions of H.M.S. " Porcupine," 

 read at a meeting of the Zoological Society of London in February 1873, I described 

 as a new genus and species, under the name of Diplo]itero7i insigne, a very beautiful 

 Plumularian dredged off the north-west coast of Spain, from a depth of 3G4 fathoms, 

 during one of these expeditions.^ 



G. 0. Sars had, however, in the same month, but a few days earlier, described under 

 the generic name of Polyplumaria, a Hydroid from the Norwegian Seas, which I believe 

 must be generically associated with the Hydroid of the " Porcupine."^ The priority of 

 description thus Hes with Sars, and though he does not appear to me to have seized on 

 the essential characters of the genus, the name Diplopteron must sink into a mere 

 synonym of Polyplumaria. 



1 have here modified the diagnosis of Diplopteron as originally given, a diagnosis 

 which, founded as it was on a single species, was too exclusive to admit forms which ought 

 not to be generically separated. In the three species of which the genus Polyjjlumaria 

 now consists, the most striking feature is the accessory ramulus, to which the hydrothecal 

 pinnse give origin. This ramulus springs from every hydrothecal pinna near to its origin, 

 and is itself composed of internodes which carry hydrothecse similar to those of the 

 pinna from which it springs. 



Sars, it is true, does not describe the accessory ramulus as constant, but as it was 

 never wanting in any of the specimens examined by me, being, on the contrary, always 

 very characteristic, I cannot but regard its absence from some of the branches in Sar's 

 specimens as accidental. 



' Report on the Hydroids collected during the expeditions of H.M.S. " Porcupine." Trans. Zool. Soc. Lond., 

 vol. viii. p. 8. 



2 G. 0. Sars, Bidrag til Kundskaben cm Norges Hydroida. Forhandl. Vidensk. Selsk. i. Cliristiania, 1873. 



