PLUMULARID^. 139 



Medusa, like Tima, swims at a considerable depth below the surface. 

 The action of the light and increase of temperature of the surface is 

 sufficient to kill them in the course of half an hour ; the moment they 

 are brought to the surface, the spherosome loses its transparency, the 

 genital organs become dull, and the Medusa is soon completely decom- 

 posed. This action is much more rapid than any thing of the kind 

 which I have noticed even in Ctenophorse, Mertensia being the only 

 genus in which the decomposing effects of light and heat are at all 

 equal to what is produced here. This Jelly-fish must be a deep-water 

 species, as they have only been found during a single fall, and then 

 only for a few days, when they seemed quite abundant. 

 Massachusetts Bay, Nahant (A. Agassiz). 



Family PLUMULARID^ Agass. 



PlumularidcE Agass. Cont. Nat. Hist. U. S., IV. p. 358. 1862. 

 Sertularidce Jojblnst. (p.p.). Brit. Zooph., p. 89. 



AGLAOPHENIA Lamx. {resfr. McCr.). 



Aglanphenia Lamx. (pars) ; in Bull. Soc. Phil. 1812. 

 Aglaophenia McCr. Gymnoph. Charleston Harbor, p. 98. 1857. 

 Aglaophenia Agass. Cont. Nat. Hist. U. S., IV. p. 358. 1862. 

 Plumularia Lamk. (^pars). Auim. s. Vert., H. p. 159. 



Aglaophenia pelasgica McCk. 



Aglaoplienia pelasgica McCr. Gymn. of Charleston Harbor, p. 99. 1857. 

 Sertidaria pelaagica Bosc. Hist. Nat. Vers., HI. p. 122. 

 Plumularia pelasgica Lamk. An. s. Vert., H. p. 167. 

 Dynamena pelasgica Blainv. Man. dActin., p. 484. 



Cat. No. 253, Florida, 1858, L. Agassiz. Hydrarium. 



Cat. No. 254, Tortugas, Fla, 1859, L. Agassiz. Hydrarium. 



Cat. No. 255, Hayti, 1858, Dr. D. F. Weinland. Hydrarium. 



Cat. No. 256, Gulf Weed, 1858, Dr. D. F. Weinland. Hydrarium. 



Cat. No. 257, Gulf Weed, 1858, Dr. D. F. Weinland. Hydrarium. 



Cat. No. 390, a hundred miles south of Cape Hatteras, A. S. Bick- 

 more. Hydrarium. 



Cat. No. 391, a hundred miles south of Cape Hatteras, A. S. Bick- 

 more. Hydrarium. 



