SCYPHOMEDUSAE 363 



285 (Gulf of Guinea, from 150-0 and 125-175-0 m.). Since P. dodecabostrycha as a 

 rule lives in greater depths of 500-1250 m., and has been found by the 'Valdivia' 

 (Vanhoeffen, 1903) in the Guinea stream at depths of 2000 and 1200 m., it seems 

 probable that the individuals caught by the ' Discovery ' in the Gulf of Guinea have been 

 transported to the surface by the cold vertical upwelling stream (" Auftriebwasser"). 



On the whole the results of our studies on the bathymetrical distribution of Periphylla 

 agree with those of most previous authors (Vanhoeffen, Maas, Mayer, Bigelow), but not 

 with those of Kramp and Broch. Kramp (1913) found in the waters of Greenland, that 

 specimens of every size may be found at every depth, but that small individuals are more 

 abundant in deeper strata, and that large specimens may occasionally ascend towards 

 the surface. This view does not agree with our facts. His results on the vertical distribu- 

 tion of the Mediterranean P. hyacinthina (1924, p. 42) correspond better. According 

 to Broch (1913)^ P. hyacinthina in the North Atlantic has a bathymetrical range from 

 50 to about 1500 m. with a somewhat prominent maximum at about 500 m. In our 

 series the limits are still wider, from the upper layers to 2500 m. According to Broch 

 the faintly pigmented dodecabostrycha prefer the shallower waters down to 500 m., while 

 in the Discovery series the maximum of dodecabostrycha occurs in a stratum of 750- 

 1000 m. According to Broch the deeply coloured typical hyacinthina predominate below 

 1000 m. In the present series they have their maximum at 750-1000 m. According to 

 Broch the intermediate group is mostly found in the intermediate waters. In our series 

 the few specimens of this type occur in the more superficial layers from 750 m. upwards. 



In Antarctic seas forma regina has been found mostly in deep zvaters by this expedition, 

 as will be seen from Table V. Browne (1910), however, records a few specimens from 

 Cape Adare and McMurdo Sound from the surface. That deep-water forms in the cold 

 regions are found at the surface is a well-known fact, and it agrees with the statements 

 about P. hyacinthina in the Davis Strait by Kramp (1924, p. 72). 



Periphylla hyacinthina proves to be a true bathypelagic medusa zvhich during its develop- 

 ment sinks slowly into deeper layers. The occasional occurrence of the dodecabostrycha 

 specimens in superficial layers in the tropical regions is perhaps to be explained by 

 cold vertical upwelling currents which carry deep-sea animals to the surface. 



1 Besides the 128 specimens of Periphylla brought home from the Atlamic the 'Michael Sars' made a 

 haul in the Sognefjord which contained no less than 1075 specimens of P. hyacinthina 1 Nobody else besides 

 Broch has possessed such an enormous quantity of fresh material of this jelly-fish. It is very much to be 

 regretted that Broch omitted the opportunity of making a thorough study of this unique material. If the 

 number of the Atlantic specimens was too small to allow him to draw final conclusions with regard to the 

 bathymetric range (p. 7), this most probably would not have occurred with the rich Sognefjord material. 

 In his report he only makes a few remarks on the strange "secondary centre" in the Sognefjord, and gives a 

 rather superficial table. 



5-2 



