9 6 



MEDUS/E. I. 



southerly parts of its area of distribution. It is possible, accordingly, that the species just described 

 will prove in time to be only a northern giant variety of a species already known to science; but as 

 long as it cannot be referred with certainty to any known species, I prefer to describe it as au inde- 

 pendent species, for which I propose the name of Phialidium islandicum, because all the specimens in 

 hand have been found in the neighbourhood of Iceland. 



3000 -\- 



1000 - - \ 



Chart XII. Finds of Phialidium islandicum nov. sp. 



The species is quite distinct from Phialidium hemisph&ricum, not only by its size and the 

 large number of tentacles, but also by the number of marginal vesicles never exceeding the number 

 of tentacles. Furthermore the mouth-lips are larger and more crenulated than in the case of P/itah'dmm 

 hemisphcertcum, and the gonads are longer. The sagittal sections through the tentacular bulbs show 

 (Plate V, figs. 2 and 3) that the ectoderm on the adaxial side of the bulb is more highly developed 

 in Phialidium hemisph&ricum than in Ph. islandicum. The trace of an abaxial process on the base of 

 the tentacular bulbs in Phialidium islandicum is not always distinct; in Ph. /lemisphcericum it is entirely 

 lacking. The shape of the marginal vesicles (see the sections, Plate IV, figs. 13 and 14) presents no 



