Chap. IV. GENEHA OF PELAGID^. 125 



eight eyes and eight tentacles between them. The best figures representing these 

 generic characters, may be found in Eschscholtz's Acalej^hs, PI. VI. Fir/. 2, a, in 

 Milne-Edwards' (Cuvier's Animal Kingdom) Zooph3'tes, PI. XLV., and in Brandt's 

 description of the Medusas observed by Mertens, PI. XIV. A, Fig. 5. The figure in 

 Wagner's Icones (PI. XXXIII. Fig. 5), though correct, has the tentacles partly so 

 turned out of their natural jjosition that their symmetry is not very obvious. 



Placois Ag. In this genus, the type of which is Pelagia discoidea Esch., each 

 marginal sac of the radiating pouches forms a small shallow lobe by itself, the 

 sacs being only short lateral prolongations of the pouches themselves ; and in con- 

 sequence of this arrangement the eyes and tentacles are nearer the margin than 

 in Pelagia proper. There are thus thirty-two small lobes, between two and two 

 of which alternate eight eyes and eight tentacles. The radiating pouches are much 

 shorter than in Pelagia pro2:>er, owing to the very extensive dimensions of the 

 central cavity. The disk is fiat and spreading, while in Pelagia proper it is hemis- 

 pherical. See Eschscholtz's Acalephs, PI. VII. Fig. 1. 



Chrysaora Per. and LeS. Type, Medusa hysoscella Lin. In this, as in the 

 preceding genus, the alternating ocular and tentacular pouches form separate lobes, 

 instead of Ijeing soldered two and two together, as in Pelagia, in consequence of 

 which the margin has thirty-two indentations; but Chrysaora differs from Pelagia in 

 this, that instead of a single tentacle in the middle, between the two lobes of the 

 tentacular pouches, it has also one tentacle in the indentation which separates the 

 tentacular and the ocular pouches ; Avhile in Placois there are none. The genus 

 Chrysaora may, therefore, be characterized thus : ocular pouches bilobed, with an eye 

 between the two lobes; tentacular pouches bilobed, with a tentacle between the two 

 lobes and another on each side of them. The consequence of this arrangement is, 

 that Chrysaora proper has twenty-four tentacles, arranged in groups of three, alter- 

 nating with eight eyes. See Eschscholtz' Acalephs, PI. VII. Fig. 2, and Milne-Edwards' 

 Cuvier's Animal Kingdom, Zoophytes, PL XLVII. Though somewhat wider, the 

 tentacular pouches have exactly the same structure as the ociilar pouches. With 

 reference to their homologies, the Medusa^ of this genus consist of four ambulacra! 

 pouches with one eye between their two marginal lobes, and four interambulacra, 

 consisting each of one genital pouch with an eye between its two marginal loljes 

 and two tentacular pouches, with three tentacles in each, one between, and two on 

 the sides of its marginal lobes. 



Dactylometra Ag. In this genus, the tentacular pouches are not only much 

 broader than the ocular pouches, but their marginal sacs present also a different 

 combination. In the ocular pouches they end in two sacs forming two distinct 

 lobes, between which are situated the eyes ; but in the tentacular pouches each 

 of the two sacs forms two lobes, and there is a longer tentacle between the two 



