286 DISCOVERY REPORTS 



records this species from Punta delle Vergine (in southern part of South America) and 

 from Punta Arenas (Pacific coast of Costa Rica), but from the figures it seems doubtful 

 whether the identification is correct. The occurrence in the south-eastern part of the 

 North Sea (Hartlaub, 1917; and Kiinne, 1933) is undoubtedly due to casual trans- 

 portation of the hydroid by ships. The hydroid was described from Kerguelen 

 Island under the name of Perigonimus macloviamis by Vanhoffen (1909), who was also 

 inclined to regard the small polyp described by Hartlaub (191 1, p. 173) as Bongo mvillia 

 superciliaris, as belonging to the genus Perigonimus. Vanhoffen therefore proposed to 

 remove the corresponding medusae from the genus Bougainvillia and only retain this 

 generic name for the medusae derived from hydroids of the same name. For macloviana 

 and superciliaris he reintroduced the generic name Hippocrene. As pointed out by 

 Stechow (1919, p. 21) and Kramp (1928, p. 50) there is, however, no reason to refer the 

 hydroids of these two species to Perigonimus; they are much more like the other 

 Bougainvillia hydroids. Moreover, the name Hippocrene was preoccupied in 18 17 by 

 Oken for MoUusca. 



The development of the medusa. The umbrella in the earliest stages is bell-shaped 

 or globular, with very thin walls (Plate XV, fig. 8). As the medusa grows the walls 

 increase considerably in thickness, and a mass of jelly is formed above the top of the 

 umbrella cavity (Plate XV, fig. 7). In the intermediate and adult stages the umbrella is 

 somewhat variable in its proportions, being either bell-shaped, of about equal height 

 and width, or cylindrical, higher than wide. To a certain extent this variability in 

 shape may be due to shrinkage in preservation. The exumbrella in the earliest stages is 

 quite smooth and even, but during the early intermediate stages interradial longitudinal 

 furrows begin to appear (Plate XV, fig. 9) and they become deep and conspicuous in the 

 adult. There are also perradial furrows, which appear a little later; they are shallow, 

 not nearly so deep as the interradial. In the jelly of the walls of the subumbrella there 

 are eight adradial ridges which appear in the early intermediate stages and are well 

 developed in the adult. Such ridges also occur in other genera and are regarded as 

 muscular bands. 



The margin of the umbrella is more or less quadrangular in all the stages, and the 

 four compound basal bulbs form the four corners. When the margin is looked at from 

 a lateral aspect, it is seen to curve slightly upwards between the basal bulbs, and the 

 basal bulbs to hang down on a slight extension of the wall of the umbrella, forming in 

 the largest adults a kind of lobe. 



The velum is very broad in the early stages, but only of moderate width in the 

 adult. 



The stomach in the earliest stages has a quadrangular base and is either cubical or 

 cone-shaped. The peduncle, which is so conspicuous in the later stages, is undeveloped. 

 In some of the earliest stages an apical stalk is present on the top of the stomach, and it 

 is the remains of the canal and stalk which connected the medusa to its hydroid. The 

 apical stalk is confined to the earliest stages and is absorbed before the intermediate 

 stages are reached. When the medusa has grown to about 2 mm. in diameter and has 



