214 ON A SPECIES OF STPHONOPHOEE OBSERVED AT PLYMOUTH. 



of the nectosac ; whereas in the Plymouth species the hydrcecium 

 extends to one third the height of the nectosac^ and the upper end 

 of the soinatocyst is above the apex of the latter. 



The third species recognised by Haeckel is one described by Huxley 

 in his Ray Society monograph on the Oceanic Hydrozoa as Diphyes 

 Chamissonis. This form was obtained in the Pacific Ocean^ and is 

 distinguished by the broader, shorter form of nectocalyx, and by the 

 denticulation of its ridges. 



Haeckel's second species is one observed by himself in the Canary 

 Islandj Lanzerote, which he says differs from M. Kochii mainly in 

 the size of the conical hydroecium, the top of which attains to half 

 the height of the nectosac. Haeckel has nowhere given a figure nor 

 any more detailed description of this species. As for its name, he says 

 it may retain the name Muggixa pyramidalis, but the choice of this 

 name seems to have been due to a mistake. In the translation of 

 Chun's paper in the Ann. and Mag. Nat. Hist., he points out that the 

 young Muggisea Kochii when first developed from the egg has not 

 the characters of Muggiaea, but of the genus Monophyes ; the necto- 

 calyx is rounded, not pyramidal, and the hydroecium is an open 

 groove, not a closed cavity. Chun calls this stage 3Ionophyes pri- 

 mordialis, which Haeckel quotes as Monophyes 'pyramidalis. On the 

 other hand, the Eudoxia stage of Muggisea Kochii was described by 

 Will under the name Erssea pyramidalis. 



Now, although it seems to me extremely probable that the form 

 observed by Haeckel at the Canary Islands was of the same species 

 as that obtained at Plymouth, it is not certain. The most charac- 

 teristic feature about the Plymouth form seems to me to be the great 

 length of the somatocyst and the position of the oleocyst above the 

 apex of the nectosac. I wrote to Professor Haeckel on the subject, 

 and he replied that he was unable after so many years to ascertain 

 whether his species and mine were the same, as he had neither 

 specimens nor drawings which sufficiently exhibited the test structures. 

 At the same time I think it is inconvenient to use for another 

 species either of the names pyramidalis or primordialis, which have 

 been applied to stages of Muggisea Kochii. I have therefore 

 to find a new name for the species occurring at Plymouth, which 

 may or may not have a range extending to the Canary Islands, and 

 will call it M. atlantica. There is one point to be noted which makes 

 it very probable that the Canary Island form and the English form 

 are the same, namely, that in the former according to Haeckel the 

 hydroecium extends to half the height of the nectosac, and in the 

 latter its relative height is nearly as great, so that in the Canary 

 Island form the somatocyst may extend as in the English to the apex 

 of the nectosac. 



