124 DISCOPHORiE. Part III. 



if my sup2)Osition that Nausithiie is a young Pelagia is correct, the middle lobe 

 of the genital pouches {b b), of my Fig. 2, are not yet developed. 



I have ventured to introduce here these remarks, Avhich may seem irrelevant, 

 in consequence of the deep conviction which has gradually grown up in my mind, 

 that there is a uniformity of plan among Acalephs far more strongly impressed 

 upon all their various types than could be inferred from the manner in which 

 they have been described, or from the manner in which they are represented. 

 I venture to make this case a test of the validity of this conviction, even though 

 I have, in so doing, to question the accuracy of so sagacious an observer as 

 Gegenbaur. 



SECTION II. 



THE GENERA OF PELAGID.E. 



Thus far the genera admitted among the Pelagidaj have been distinguished by 

 the number of their tentacles, Pelagia proper containing those with eight tentacles, 

 Dodecabostrycha those with twelve, Heccaedecabostrycha those with eighteen, and 

 Polybostrycha those with twenty-four or more tentacles. As characterized by Peron 

 and LeSueur, the genus Chrysaora is very indefinite, as he simply .assigns to it a 

 peduncle perforated in the centre, entirely distinct arms, which do not branch, and 

 a lai'ge central cavity. Eschscholtz has characterized it more j^recisely, by showing 

 its affinity with Pelagia, as foimded upon the pouch-like ajjpendages of the main 

 cavity and the insertion of the tentacles, which are more numerous. On this last 

 account, however, Eschscholtz, who considers the number of tentacles as of trifling 

 importance, is inclined to regard Chrysaora as hardly generically distinct from 

 Pelagia; l)ut if, instead of considering only the number of these appendages, we 

 take into account their connection with the lobes of the margin, it will be at 

 once apparent, not only that Chrysaora, as defined by Eschscholtz in imitation of 

 Peron and LeSueur, is a distinct genus, but that it embraces, like Pelagia, several 

 distinct generic types. 



Pelagia proper embraces all those species thus far referred to the genus, which, 

 like Pelagia noctiluca, cyanella, and panopyra, have sixteen equally developed 

 pouches, each of which branches off into two distinct sacs near the margin, and are 

 there so combined that the marginal lobes embrace one sac of two adjoining 

 pouches, and that in the indentations dividing these lobes there are, alternately, 

 one eye and one tentacle, the whole margin being divided into sixteen lobes, with 



