MKDUSiE. 143 



When a medusa lias normally six radial canals, a variation in number may be 

 expected. Medusae with six radial canals have been derived from a form with four 

 canals, and are much more liable to variation than those with fQiir canals. There are 

 altogether 27 specimens of Irenopsis, and six show a numerical variation in the radial 

 canals, their numbers being as follows ; 4, 7, 8, 8, 9, 11. The number of gonads also 

 varies with the radial canals. The gonads vary very much in size, and are always 

 situated upon the distal or outer half of the radial canals. Most of the specimens 

 have very short linear or spindle-shaped gonads, about 1 millim. or little more in 

 length, and situated near the margin of the umbrella. Three specimens have the 

 gonads extending over nearly the whole of the distal half of the canals, but not quite 

 reaching to the margin of the umbrella. 



The tentacles vary in number according to the size and age of the specimens. The 

 exact number in any one specimen could not be ascertained, as all the specimens have 

 the margin of the umbrella more or less damaged. As a rule, in the largest specimens, 

 there are about five or six tentacles (one specimen has six or seven) between every 

 two radial canals. I estimated the number of tentacles in several large specimens to 

 be about 36, and in one specimen at about 40. About the exact shape of the basal bulbs 

 of the tentacles I am uncertain. In a contracted state they look somewhat globular, 

 but are probably more conical when the tentacle is expanded. The marginal bulbs 

 between the tentacles are very minute and their number is variable. Usually about 

 three are present, but occasionally only one between every two tentacles. There are 

 excretory pores opening above the velum, opposite every basal and marginal bulb. In 

 nearly every specimen these pores are so contracted that their presence is not 

 noticeable. In a few specimens they are well expanded (fig. 5) and form long papillae. 

 The marginal sense-organs (fig. 7) are closed vesicles, usually with a single otolith, 

 but occasionally with two or three otoliths, rarely with four. There is generally only 

 one ' between every two marginal bulbs, or about two to four between every two 

 tentacles. 



The genus Irenopsis was established by Goette for Irenopsis hexanemalis, found 

 at Zanzibar. The original description is rather brief and there is no figure. Chun, 

 however, has given a fuller account of some specimens taken at Tumbatu, off 

 Zanzibar. The genus clearly belongs to the sub-family Irenidae, and is readily 

 distinguished by the presence of six radial canals. As the specimens from Ceylon 

 agree with the descriptions given by Goette and by Chun, I have presumed that 

 they are Irenopsis hexanemalis, though I should have liked to see a figure for 

 comparison. 



After seeing these specimens of Irenopsis I again examined Phialidium tenue, 

 which was described by me as a new species in the Report on the Hydromedusae of 

 the Maldive Islands. The description of this species, based upon a single specimen, 

 was given as follows : " Umbrella watch glass- shaped and thin. Stomach small, 

 quadrangular in shape, and situated on a semi-globular thickening of the umbrella. 



