T 



SCYPHOMEDUSAE 



By G. Stiasny, D.Sc, Leiden 

 (Plates XIV, XV; text-figs. 1-12) 



INTRODUCTION 



HE present paper is a report on Scyphomedusae, based on collections made by the 

 R.R.S. 'Discovery' and R.R.S. 'Discovery IT and to a smaller extent by the 

 R.R.S. 'William Scoresby'. The cruises of these ships took place in the years 1925 to 

 193 1, and followed a route along the West African coast, but chiefly in the Southern 

 Atlantic and Antarctic Oceans, fishing at depths ranging from the surface down to 

 about 2500 m. The study of the present collections produced no surprising results. 

 They are not rich with regard to the number of different species, and contain no new 

 forms. The present catches are, however, important for other reasons. They are made 

 especially in a region of the South Atlantic between 30 and 55° S Lat., hardly explored 

 with regard to Scyphomedusae. The previous expeditions (those of the 'Challenger', 

 'Valdivia', 'Scotia' and 'Gauss') paid occasional visits only to this area; the hauls 

 made were very few and dispersed, and mostly single specimens of Scyphomedusae 

 were caught. 



The 'Discovery' and 'Discovery 11', however, obtained large series of some forms 

 {Periphylla and Atolla), the study of which made it possible to settle certain systematic 

 problems, to fill up a gap in our knowledge of the geographical and bathymetrical dis- 

 tribution, and to add in this way not inconsiderably to our knowledge of the Scypho- 

 medusan fauna of the South Atlantic. A rich collection of the rare Atolla chimi, 

 Vanhoeffen, has been gathered, only three specimens of this form having hitherto been 

 known. The importance of the Discovery collection is augmented by the fact that it 

 enables us to compare the results of the studies of these catches with those made by 

 the ' Michael Sars ' in the North Atlantic. In many respects the Michael Sars collections 

 form a counterpart to those of the 'Discovery'. Just as the 'Michael Sars' explored a 

 boreal region between 20 and 60° N Lat., the 'Discovery' examined the sub-tropical 

 and sub-Antarctic waters of the southern part of the Atlantic in a belt of the same 

 breadth. In both cases the bulk of the collected specimens is made up of a large 

 number of Periphylla and Atolla. The ' Discovery ', however, obtained a much smaller 

 number of Pelagia than did the 'Michael Sars' (Broch, 1913). 



The results and conclusions reached by Broch on the relation between the increase 

 of quantity of pigment, size and number of individuals and the increase of depth, could 

 be checked and controlled with the rich series of Periphylla and Atolla. It was found 

 that Broch's conclusions could be confirmed in some respects, but that in others they 

 must be regarded as going too far. One of the most important results of Broch's studies 

 was that the material brought home by the 'Michael Sars' demonstrates that the 



