272 DISCOVERY REPORTS 



In the earliest stage the umbrella is bell-shaped and the exumbrella is covered with 

 scattered nematocysts. The subumbrella cavity (Plate XIV, fig. 2) is very small owing to 

 the bulging in of the wall of the umbrella, and perradially the wall is nearly cut through 

 by four deep longitudinal grooves which extend to the radial canals, close to the 

 exumbrella. In a transverse section the umbrella cavity is distinctly cross-shaped. The 

 perradial grooves are only just visible in the adult owing to the increase in the thickness 

 of the umbrella wall. As the medusa passes through the intermediate stage a second 

 series of shallow grooves appear, interradially situated. In addition to these longitudinal 

 grooves along the wall of the subumbrella, there are eight adradial ridges in the sub- 

 stance of the umbrella wall. 



The gonads extend nearly from the base of the manubrium to the mouth and com- 

 pletely surround the tube-like stomach. The tentacles are rather thin and not of great 

 length ; when contracted they are about the same length as the umbrella, but in well- 

 preserved specimens with extended tentacles they may be twice as long. The upper part 

 of the tentacle next the basal bulb is free from nematocysts ; beyond this naked portion 

 nematocysts are present in small roundish groups, evenly distributed on all sides of the 

 tentacles ; towards the distal end these groups are confluent, forming transverse bands 

 gradually increasing in breadth, and in the extreme portion of the tentacle they often 

 form complete rings, especially in younger individuals ; the number of complete rings of 

 nematocysts is very variable, but seldom exceeds five or seven. The free end of the 

 tentacle terminates in a large round knob, full of nematocysts (Plate XV, fig. i). The 

 basal bulb of the tentacles is small, and a moderate-sized roundish ocellus is situated on 

 the outer side close to the exumbrella. 



The velum is very broad and has a small circular opening. 



Remarks. Mayer (1910, p. 60) indicates the possibility of Sarsia gracilis being a young 

 Slabberia ; as, however, several of the specimens from the Falkland Islands are sexually 

 mature, this supposition cannot hold good. The genus Slabberia is characterized by 

 the gonads forming two or more separate rings around the manubrium. 



The most characteristic feature of Sarsia gracilis is the presence of a prominent knob 

 of nematocysts in the terminal end of each tentacle ; a similar structure is found in the 

 following species of Sarsia: (i) S. coccometra Bigelow (1909, p. 179, pi- 7- %• ^ 5 P^- 4°. 

 fig. I ; pi. 43, figs. 8-9), from the Pacific coast of Central America, is about the same size 

 as S. gracilis, the umbrella has a large, pointed apical projection, the manubrium is very 

 broad and thick, and above the terminal knob (which is not very prominent) the ne- 

 matocysts form complete rings throughout the whole length of the tentacle, (ii) S. inabai 

 Uchida (1933, p. 126, fig. 2) from Kamtchatka has very short tentacles with an egg- 

 shaped terminal knob but no other groups of nematocysts. (iii) S. nipponica Uchida 

 (1927, p. 183, pi. 10, fig. i) from Kishu, Japan, seems to be the species nearest related 

 to S. gracilis; it is much smaller, only i-2 mm. high, and fairly broad in proportion to its 

 height; the tentacles are short and have only six or seven groups of nematocysts. The 

 common European S. gemmifera Forbes is distinguished from all these species by its 

 very long and thin manubrium, from which budding of medusae takes place. 



