ATLANT. DEEP SEA EXPED. 1910. VOL. III]. 



SCYPHOMEDUSAE. 



19 



deeper layers having probably been caught 

 while the gear was being hauled in. 



At Stats. 84, 90, 92 and 94 the species was 

 not found at the very surface, and at first I 

 thought this might be due to the time of day 

 when the hauls were taken, but during the same 

 hours of the day at other stations Pelagla was 

 abundant at the surface. Stations 90, 92 and 94 

 were evidently near the northern limit of the 

 species, and this may explain its scarcity in the 

 surface waters. 



The geographical data obtained during the 

 cruise explain some interesting points in the 

 life-history of this holoplanktonic medusa. P. 

 perla is a tropical and subtropical species, which 

 is carried northward by the Atlantic current; its 

 habitat is limited by the arctic currents, and it 

 is therefore missing over the Newfoundland 

 banks, and a rare guest in Norwegian waters. 

 It is remarkable that the medusa was rather 

 scarce throughout the southern part of the route 

 of the "Michael Sars" (see iig. 11); only at Stat. 

 56, south of the Azores, was a larger shoal met 

 with, consisting almost entirely of very young stages. 

 Such large shoals of Pelagia are commonly found where 

 currents meet, as has been pointed out by most of the 

 previous authors. On the other hand, older stages were 

 far more abundant in the northern section than at Stat. 

 56, probably because at most places in the southern 

 section the time of reproduction had not fully set in 

 when this part of the sea was explored. 



Chrysaora Peron and Lesueur. 

 Chrysaora mediterranea Peron and Lesueur. 



In the Bay of Algeciras the umbrella of a medusa 

 was taken on the 1. of May. The umbrella is 75 mm 

 broad, with narrow, brown radial stripes, the central parts 

 of the disc light yellowish, and each lappet with a large, 

 dark brown spot in the centre. The margin is perfect, 

 but of the tentacles only the basal parts are left. Every 

 trace of gonads and stomach has disappeared, but never- 

 theless the bell may easily be identified as belonging to 

 Chrysaora mediterranea. 



It is still an open question whether C. mediterranea 

 is specifically distinct from C. hysoscella (Lin.), as Van- 

 hOffen 1 ) has pointed out. Judging from the locality I 

 prefer at present to refer this defective specimen to C. me- 

 diterranea, with the description of which it agrees quite well. 



© Occurrence of Pelagia perla during the cruise of the 



Fig. 11. 



'Michael Sars". 



Poralia Vanhoffen. 



This genus was established by Vanhoffen 2 ) for a 

 defective medusa taken by the "Valdivia" in the vicinity of 

 Sumatra. Our knowledge of this primitive and interesting 

 genus was considerably widened by the investigations of 

 Bigf.low, 3 ) who had an opportunity of examining two 

 damaged specimens taken by the "Albatros" in the 

 eastern Pacific. 



At Stat. 85 (Lat. 47° 58' N, Long. 31° 41' W) a very 

 much damaged specimen of a Poralia, was caught in a 

 Nansen's closing net between 2000 and 1100 metres. 

 This specimen probably belongs to P. rufescens Vanhoffen, 

 the only known species, and consists of the central parts 

 of the disc, with undivided radial canals, and a damaged 

 stomach. These parts correspond to the descriptions given 

 by Bigelow (1. c). The subumbrella is of a dark brownish 

 colour; on account of their somewhat lighter colour the 

 32 radial canals stand out distinctly. Every trace of the 

 ring-canal described by Bigelow has disappeared. In 

 fact, we can do no more than record the presence of 

 the genus Poralia in the Atlantic, but this is of great 

 interest, when we consider the previously known localities 

 for the genus (see fig. 12), which seems to be tropical 

 and subtropical and circumterrestrial, and a true deep- 

 sea form. 



') Acraspede Medusen (Nordisches Plankton Lief. V.). Kiel 1906, p. 47. 



2 ) Die Acraspeden Medusen. (Wiss. Ergebn. Deutschen Tiefsee-Exped. Bd. III). Jena 1902, p. 40. 



3 ) The Medusae (Rep. scient. res. eastern tropical. Pacific "Albatross".— Mem. Mus. Comp. Zool. Vol. XXXIII). Cambridge U.S. A. 1909, p. 44. 



