THE MEDUSA. 



165 



of Atolla, one of those medusae which are generally found at great depths and in cold 

 water ; and two early stages of a Periphylla, which is another medusa belonsins to the 

 deep and cold zone. 



The Anthomedusaj are represented by a single species, namely, Margells autumnalis, 

 and the Leptomedusse by two species — Obelia Incifera and a T'mia. The occurrence of 

 these medusae so far from the coast is no doubt due to a siu-face-drift. They are neritic 

 species which have gone astray. Fragments of the common littoral hydroid Campanu- 

 laria fiexuosa were also taken in the tow-net. 



Comparison with the Medusa recorded for the English Channel. 



I should not have attempted a comparison with the medusae of the English Channel, 

 but for the results which have been obtained by an investigation of the plankton of the 

 Channel by the Staff of the Marine Biological Association at Plymouth. In 1903 a 

 series of quarterly cruises was begun in connection with the International Fisheries 

 Investigations. On these cruises series of tow-nettings are taken at definite stations, 

 some of which have been arranged to cover the entrance to the Channel. 



Until the cruises began our knowledge of the Channel medusae was limited to those 

 found about twelve miles from shore, consequently nearly all the species which have 

 been recorded belong either to the Anthomedusae or Leptomedusae ; a list compiled for 

 these two orders gives about forty-five species. The Trachomedusae are represented by 

 only two species, namely, Liriope {Liriantha) tetraphylla, which occasionally comes in 

 shoals, and Gossea corynetes, which is rather scarce. The Narcomedusae are seldom 

 seen close in shore, and only one species {Solniaris corona) has been recorded. 



The results obtained on the quarterly cruises for the years 1903, 1904., and the first 

 half of 1905 have been rather disappointing so far as medusae are concerned. Up to 

 the present Aglantha rosea is the only new addition to the list. I certainly expected to 

 see a greater increase of species among the Trachomedusae and Narcomedusae. 



Gough (1905) in his account of the distribution of individual species in the Channel 

 says : " a comparison of the ranges of the single plankton-elements demonstrates the fact 

 that the oceanic species invade the Channel from the south-west, and become rarer as 

 they advance up the Channel." Now Dr. Fowler's stations lie in the track of meduste 

 invading the Channel from the south-west, so one would expect to find some of the 

 Biscayan species at the mouth of the Channel. For a comparison it is necessary to omit 

 the species which are known at great depths, and select only those which occur within 

 100 fathoms of the surface, as the depths of the Channel stations do not exceed 

 90 fathoms. We have then the following three species — Aglantha rosea, Aglaura 

 hemistoma, and Bhopalonema coeruleum — living within 100 fothoms of the surfocc in the 

 Bay of Biscay. Aglantha i^osea has succeeded in entering the Chamiel, but the other 

 species have not. The records, up to the present, of the medusae taken at the entrance 

 of the Channel are distinctly in favour of the neritic forms. It appears that the oceanic 

 species only now and again drift within the Channel area. 



