sr.M MIMSTMMK.E PELAUl \. 



571 



seems probable that the foldings observed by Vanhoffen in the nettle-warts are largely due 

 to shrinkage in alcohol. 



The medusae of Pelagia, being pelagic in all stages, are creatures of the high seas; and 

 one would expect the species to be of world-wide distribution and at the same time to have 

 developed many local varieties which are not very clearly differentiated from their parent 

 stocks. I believe that all of the forms may be grouped into 4 cohorts as follows: 



(1) P. nocliluca, ncglecta, and crassa, of the Mediterranean and Atlantic, with large, elongate nettle-warts over the 



exumbrella. 



(2) Allied to (i ) in the Pacifir. we tin I /'. favtola, Jenticulata, laliitiaaa, and fafillala with large oval, erect nettle-warts. 



(3) P. cyanflla, ferla, diicoidea, phoipliora and minuta of the Atlantic with small, rounded nettle-warts. 



(4) P. panopyra and placenta of the Pacific with small, flatly dome-like nettle-warts. 



Cohorts (i) and (2] are closely related; and (5) and (4) form another group. 

 As in Cyanea and AurAlia so in Pelagia we find that the Linnean system is inadequate 

 to express the relationship of the numerous, closely related forms. 



Synopsis of the Forms of Pelagia. 



*Development without alternation of generations. 



tDevelopment through a pelagic larva without alternation of generations. 



JToo imperfectly known to be retained. 



The remarkable development, which is direct, without a sessile larval stage, is described 

 in detail under P. noctiluca anil /'. cyanella. The young medusa passes through a 4-tentacled 

 stage, before acquiring its 8 adradial tentacles. 



"Zonephyra corona" Agassiz and Mayer, 1902 (Mem. Museum Comp. Zool. at Harvard 

 College, vol. 26, p. 157, pi. 4, figs. 19, 20), is probably a young Pelagia. 



