MEDUSA. I. 



43 



tentacle bears, on its abaxial side, a narrow, pointed, entodermal spur, penetrating into the gelatinous 

 substance close to the exumbrellular side (Plate II, fig. 10). The distal part of the tentacle is, as a rule, 

 spirally coiled. The tentacles are very numerous and, frequently, so densely crowded that, owing to 

 the lack of room, they seem to be situated in somewhat different height on the bell-margin. 



In the young medusa the tentacles are developed in a certain regular succession, as demon- 

 strated by A. Agassiz (1863). In older specimens we find tentacles of every size in quite irregular 

 succession. We may find, however, fully developed tentacles and quite young tentacles almost regularly 

 alternating, particularly in very large specimens. When the tentacles are very densely crowded, these 

 young tentacles may be quite thin and delicate, almost like cirri, and apparently situated a little inside 

 the fully developed tentacles. By closer examination, however, we will always find that the small 

 tentacles are not quite alike, but that some of them are a little larger than the others and approach 

 the fully developed tentacles in shape. When there is a little better room, the young tentacles are 

 placed in the same row as the others and have a fairly broad base, clearly indicating that they are 

 real tentacles, not cirri; besides, a spur is very soon developed. Ocelli, on the other hand, are usually 

 not developed until the tentacle has reached a fairly considerable size. The nearly regular alternation 

 of small tentacles without ocelli and large tentacles with ocelli was the feature, on which Browne 

 (1908, p. 235) based the species Staurophora falklandica. As exactly the same feature is frequently found 

 in northern specimens of Staurophora, and as Staurophora falklandica in all other respects has a 

 complete likeness to the northern Staurophora mertenstt, there can be no doubt as to the identity of 

 the two forms. Browne himself remarks (p. 236): "It is rather a risky point, I admit, on which to 

 base the character of a new species, as there is the probability of the small tentacles developing into 

 full-sized tentacles with ocelli". 



As a rule, there is one adaxial ocellus on the base of each of the tentacles with the exception 

 of the quite young ones. Some irregularity may, however, be found. In 4 specimens from North-Iceland 

 ("Thor" stat 220(04), Loc. No. 5) the ocelli are arranged in the following manner: i) Diameter of the 

 specimen 8 cm, ocellus on about every 4th of the tentacles; 2) diameter 9 cm, ocellus on about every 

 3rd 4th of the tentacles, not seldom two ocelli on one tentacle; 3) diameter 10 cm, ocellus on every 

 3rd -4th of the tentacles; 4) diameter n cm, ocellus on almost every 2nd of the tentacles. Sometimes 

 the pigment of the ocelli may disappear on account of the preservation, and we cannot exclude the 

 possibility that this has happened in the specimens mentioned above, as far as' the tentacles now 

 destitute of ocelli are concerned. 



In this species the number of cordyli (Plate I, fig. 9; Plate III, fig. 7) is always equal to the 

 number of tentacles, the cordyli regularly alternating with the latter, situated in a row a little inside 

 the row of tentacles. The peduncle is thin and lengthened, the distal part is fairly much swollen. With 

 regard to the question of their transformation into tentacles, see above, p. 5. 



The velum is very narrow, i 2 mm broad. 



According to the literature this species may attain - a size of 20 cm in diameter. Among the 

 material in hand no specimen is more than about 12 cm wide; this is probably due to the collectors 

 having not, for lack of room, preserved the largest of the specimens found. I remember having seen 

 numerous very large individuals, far more than 12 cm wide, in the waters round Iceland in 1908. 



