810 Proceedings of tJie Royal Irish Academy. 



and that they certainly do not agree with S. octoradiatus, for 

 the largest of them, though only half as hig as full-sized 

 specimens of the latter, have already as many, or even more, 

 tentacles on each arm and saccules in a genital hand than the 

 maximum number given for that species ; and the saccules are 

 different in arrangement as well as in number. The fact that 

 sexual maturity may be attained in a Medusa before it has 

 reached its maximum growth and development has been recog- 

 nised by Browne^ among the Hydromedusse ; more especially 

 in the case of Li%%ia llondina, where it has led to young stages 

 of the same animal being described not only as distinct species 

 but even genera. 



Dealing now with the other characters : the approximation 

 of the arms in pairs is exhibited, more or less, by all the speci- 

 mens which I had examined with respect to this point. It can 

 hardly be regarded as a point of much value unless very 

 strongly marked ; it is shown in varying degrees by different 

 specimens, and I am inclined to think by the same individual 

 in different states of expansion, being influenced by the state 

 of contraction of the muscle-bands. The marginal anchors are 

 very variable in size. Of two equal-sized individuals, one may 

 have anchors twice as large as the other. They are sometimes 

 egg-shaped in preserved specimens, showing little or no trace 

 of a longitudinal fuiTow ; but usually they are much wrinkled, 

 especially if large, and a longitudinal furrow is visible in many. 

 In living animals which I have examined there is in most cases 

 a well-marked longitudinal furrow, suggesting resemblance to 

 a coffee-bean ; and a ring of pigment surrounds a pale and often 

 slightly raised spot, which marks the vestige of the tentacle 

 head possessed by the anchor in its early stages. These features 

 are not quite so conspicuous as in James Clark's figui'es (Mono- 

 graph, PI. i., fig. 17), but they agree very closely. Apparently 

 in our specimens the anchors assume the adult condition when 

 the animal is of smaller size than is the case in the American 

 form. Bat the size at which this takes place is by no means 

 constant. I have come across a few specimens, 6 mm. in 

 diameter, having capitate anchors, resembling James Clark's 

 figs. 25-27, PI. iii., while most individuals of that size have 

 anchors of adult form. According to Hornell {loc. cit.) a large 



1 Journ. Mar. Biol. Assoc, 1898, vol. v., p, 188. 



