REPORT ON THE DEEP-SEA MEDUSAE. 113 



also very interesting and important, since it forms a wide coronal sinus in its proximal 

 part, as in the Peromedusse. This sinus, as in Nauphanta, communicates at its distal 

 margin with the marginal corona of pouches, and at its proximal margin by four 

 perradial gastral openings with the central stomach. This original arrangement has 

 disappeared in most of the other Discomedusse, as the four interradial septal nodes 

 between the gastral openings have undergone retrograde formation, and the four 

 perradial gastral pouches separated by them are therefore no longer present ; both these 

 and the coronal sinus have consequently become merged into the central stomach. 



Atolla wyvittii, Hseckel (PL XXIX.). 



Umbrella, quite flat, discoid, about six times as broad as high. Radius of the 

 central umbrella disk almost twice as large as that of the peripheric corona of the 

 umbrella ; disk and corona separated by a very deep coronal furrow. (Esophagus, 

 constricted in the middle, quadrangularly prismatic, two to three times as broad as high. 

 Genitalia, eight elliptical pouches, grouped in pairs, in the periphery of the oesophagus, 

 their perradial distances less than the interradial, 19 to 22 (16 to 32 ?) rudimentary 

 sense clubs, and the same number of short tentacles (half as long as the radius of the 

 umbrella) alternating with them. Tentacular pedalia broader and shorter than the 

 rhopalar pedalia. Rhopalar canals rudimentary, much narrower and shorter than the 

 tentacular. Marginal lobes elliptical and obtuse. Horizontal diameter of the umbrella, 

 58-66 mm.; vertical diameter, 10-12 mm. 



Habitat. — Antarctic Ocean of the eastern and western hemispheres, in a depth of 



about 2000 fathoms. The Challenger captured five specimens of this remarkable species, 



which I was able to examine, preserved in spirits. The state of preservation was 



unfortunately only imperfect, in spite of the tough nature of the body, the epithelia 



being almost entirely wanting. All five specimens were mature females. Three of these 



were taken on 3d March 1874. Lat. 53° 55' S., long 108° 35' E. Depth, 1950 fathoms. 



Station 157, in the Antarctic Ocean nearly in the middle between the Kerguelen Islands 



and Melbourne. The two other specimens were taken 11th February 1876. Lat. 



42° 32' S., long 56° 27' W. Depth, 2040 fathoms. Station 318, South Atlantic Ocean, 



St Mathias Bay, not far from the coast of Patagonia. Bottom temperature, 0*4° C. The 



three Indian- Antarctic and the two Atlantic-Antarctic correspond completely in structure 



and show no specific difference. The horizontal umbrella diameter in the first three (from 



Station 157) amount respectively to 66, 68, and 50 mm. ; the diameter of the last two 



(from Station 318) to 40 and 38 mm. The smallest specimen of the latter (38 mm.) 



had only 19 tentacles and 19 pairs of lobes ; all the four other specimens had 22 tentacles 



and 22 pairs of lobes. I have named this highly interesting species after Sir Wyville 



Thomson, the scientific director of the Challenger expedition. 



The umbrella (figs. 1-4) of Atolla wyvillii forms a circular, thick, perfectly flat disk, 



(ZOOL. CHALL. EXP. PART XII. 1881.) M 15 



