PLUMULARIDJE. 139 



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

 The action of the light and increase of temperature of the surfoce 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 comjiletely decom- 

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

 Avhich I have noticed even in Ctenophora?, 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. 



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

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



AGLAOPIIENIA Lamx. {resfr. McCr.). 



Aglaophcnia Lamx. (parx) ; in Bull. Soc. Phil. 1812. 

 Atjlaophenia McCk. Gymnoph. Charloston Harbor, p. 98. 1857. 

 Aylaophc.ma AfiASS. Cont. Nat. Hist. U. S., IV. p. 358. 1862. 

 Plumularia Lamk. (^pars). Anim. s. Vert., II. p. 159. 



Aglaophenia pelasgica McCr. 



Aglaophenia pelangka ^IcCr. Gymn. of Charleston Harbor, p. 99. 1857. 

 Serlularia pela.il/ica Bosc. Hist. Nat. Vers., HI. p. 122. 

 Plumularia pelasgica Lajik. An. s. Vert., II. p. 167. 

 Dynamena pelasgica Blaixv. Man. il'Actin., 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. 



