302 DISCOVERY REPORTS 



LIMNOMEDUSAE 



Family WILLIIDAE 



Genus Willia Forbes (1846) 



Generic characters. Williidae with six or more radial canals, each having one or 



more lateral branches (youngest stage without branches), all running to the margin of 



the umbrella. Stomach with six or more lobes. Gonads surrounding the stomach and 



extending along the lobes of the stomach. 



The other genus of this family, Proboscidactyla Brandt, is distinguished from Willia 

 by the possession of only four stomachal lobes and four main radial canals. A revision 

 of the species of Williidae was carried out by Browne (1904, p. 724) ; as pointed out by 

 Thiel (1938, p. 302) a new revision is, however, desired. The species described below 

 even tends to efface the limits of the two genera. 



Willia mutabilis Browne 1902 (Plate XIV, figs. 8-9 ; Plate XVII, figs. 10-12 ; Plate XIX, 



fig. 12; Figs. 2-12). 



Willia mutabilis Browne, 1902, p. 280. 



Willia mutabilis Browne, 1904, p. 729. 



Willia mutabilis Browne, 1908, p. 235. 



Willsia mutabilis Mayer, 1910, p. 194. 



} Willia mutabilis Vanhoffen, 1912, p. 7, text-fig. 2. 



Willsia mutabilis Thiel, 1938, p. 302. 



Specific characters. Adult: Umbrella slightly conical in shape, with a broad round 

 summit, about as broad as high ; margin slightly inverted. Stomach small, with six or 

 eight lobes. Mouth with a closely folded margin. Six or eight main radial canals, each 

 with three or more branches, all running to the margin of the umbrella. Gonads sur- 

 rounding the stomach and the lobes of the stomach. Twenty-four tentacles or more 

 (maximum number counted fifty-four). Colour: Stomach and gonads yellowish brown; 

 basal bulbs of tentacles dark brown or black (specimens in formalin). Size: Umbrella 

 6 mm. in height and 6 mm. in width (largest specimen). 



Numerous specimens were collected in Stanley Harbour from November 1898 to 

 February 1899 and from 13 November 1901 to 22 March 1902. They show various 

 stages in development, and a great variation in the radial canal system and in the 

 number of lobes to the stomach. As a matter of fact, they show so much variability 

 that the normal characteristics of the species remain doubtful. It has normally eight 

 branched radial canals, but frequently six, and the number varies from five to eleven. 



The umbrella in the early stages is bell-shaped ; it broadens as it grows and becomes 

 somewhat cone-shaped. The walls of the umbrella are thick, and the upper third or 

 half is solid. The velum is narrow. In the exumbrella, near the margin and between 

 the tentacles, there are clusters of nematocysts (Plate XVII, fig. 10), and as the umbrella 

 grows downward the clusters remain on the exumbrella. Similar clusters are found in 

 the exumbrella of Willia stellata and of the species of Proboscidactyla. Their structure 



