NARCOMEDUSAE 67 



variable in each species. In P. clam the number increases considerably with the age of the individual; 

 especially in middle-sized specimens, several of the tentacles are usually smaller than the others, 

 sometimes even almost regularly alternating with the fully developed tentacles. The same applies in 

 a lesser degree to P. laevis. In the other species the full number is usually attained in young stages. 



The NUMBER OF OTOPORPAE is likewise an important character; it is somewhat variable in each 

 species, but apparently it increases only slightly with age. Their length is very characteristic, but has 

 been utterly disregarded in the older literature. Unfortunately in badly preserved specimens the 

 otoporpae are frequently more or less destroyed, so that it is difficult or even impossible to see them. 

 Sometimes the sensory clubs are better preserved than the otoporpae, but they do not seem to be of 

 use in the identification of species. 



The WIDTH OF THE PERIPHERAL CANALS is a character of great importance for distinction between 

 the species; it is rarely mentioned in the descriptions in the literature. 



In my attempts to identify the numerous specimens of Pegantha in the Discovery collections, 

 I proceeded in the following way. I first looked out for well-preserved specimens, which might serve 

 for a provisional orientation, and then the samples were picked out at random regardless of their 

 geographical origin. In each sample every specimen was measured, the tentacles counted, the number 

 of sensory clubs and length of otoporpae determined as far as possible, and notes made on the shape 

 of the umbrella, the softness or rigidity of the gelatinous substance, the outline and relative length 

 of the marginal lappets, the width of the peripheral canals, and the conformation of the interradial 

 diverticula and the gonads if they had attained a degree of development which made a description 

 possible. All these observations were written on labels which afterwards were arranged in groups 

 according to the various characters. Some few specimens could immediately be separated as belongmg 

 to P. triloba, and one agreed perfectly with P. nibiginosa. The remaining specimens, by far the most 

 numerous, turned out to represent three well-defined types which could be referred to the three 

 species martagon, laevis and clara, as described in Bigelow's papers after 1909. When in the end 

 I marked the localities on maps, I found that all these three species occurred in tropical and subtropical 

 seas, and that all the specimens taken south of latitude 50° S had been determined as P. martagon. 



Pegantha martagon Haeckel 1879 



(Plate VI, fig. I, text-fig. 10) 



1879 Pegantha martagon Haeckel, p. 333. PI. 19, figs. 4-7. 



1904 Pegantha simplex Bigelow, p. 260. PI. 5, figs. 19-20. 



1909 Pegantha martagon Bigelow, p. 83. Pi. 18, figs. 1-8. 



1910 Pegantha martagon Mayer, p. 443. Text-figs. 195, 196. 

 1918 Pegantha martagon Bigelow, p. 395. 



1940 Pegantha martagon Bigelow, p. 308. 

 1955 Pegantha martagon Kramp, p. 277. 



Occurrence: Stns 87, 100, 129, 133, 139, 276, 282, 284, 319, 344> 569- 593- 595- 663, 665, 667, 671, 690, 697, 

 700, 701, 709, 715, 903, 948, 972, 976, 1374. 1568, 1574. 1581, 1606, 1759, 2067. WS 28, WS 35. WS 63, WS 181, 

 WS 186, WS 187, WS 283, WS 286. (For details of position, date, etc., see Table i, p. no.) 

 Stns 903, 948, 972 and 976 are in the South Pacific between 50" S and 60° S; Stns 569, 593 and 595 

 are in the antarctic area west of Graham Land; Stns 120, 133, 139. 319- 344 and 665 and all the 

 'William Scoresby' stations are in the neighbourhood of South Georgia, 667 and 671 somewhat 

 farther to the north-east. Stns 1374, 1568, 1574, 1581 and 1759 are off the east coast of Africa between 

 about 3 5° S and 8° S. The other stations are scattered on both sides of the Atlantic Ocean between about 

 39° S and 24° N (St. 2067 between the Cape Verde and the Canary Islands) (see chart, text-fig. 10). 



