Boone, Coelenterata, Cruises of "Eagle" and "Ara," 1921-28 29 



Color: Louis Agassiz records that this medusa is highly phos- 

 phorescent at night and that the phosphorescence takes place in the 

 substance of the nervous cord. The northern form varies in color 

 from nearly colorless specimens to some that are exquisite transparent 

 violet fringed around the margin with fine tentacles of a darker violet. 

 The southern form is decidedly pinkish. 



Life history: The young of this species were first described by 

 Agassiz (1865). Mayer (1910) also described the young. 



Technical, description : Adult : Northern form. Disk, axial diam- 

 eter 10 to 15 inches; aboral surface flat or slightly concave in the 

 middle region; gelatinous substance hyaline, rigid, about three-quar- 

 ters of an inch thick in the middle of umbrella, abruptly quite thin 

 near the margin ; velum rudimentary. Eighty to one hundred chymif- 

 erous tubes present, with three to four very long, retractile tentacles 

 with hollow bulb-like ends between each two chymiferous tubes. The 

 excretion papillae are near the bases of the tentacles and some occur 

 between them. There are eight to ten very minute lithocysts, each 

 containing two spherical concretions, situated between each successive 

 pair of tentacles. There is also a single row of six to fifteen solid, 

 rounded papillae on the subumbrella, between each successive pair of 

 radial canals. The stomach is sac-like, broad proximally, tapering to 

 an elongated, cylindrical throat-tube, margined by long oral tentacles 

 which equal or slightly exceed in number the radial canals. 



References: Medusa aequorea Fabricius, Fauna Gronlandica, no. 



357, 1780. 

 Medusa globularis Modeer, Nova Acta Phys. Med. Bd. 8, p. 33, 1791. 

 Aequorea gronlandica Peron and Lesueur, Ann. Mus. Hist. Nat. 



Paris, tome 14, p. 339, 1809.— Lesson, Zooph. Acal., p. 313, 1843. 



Aequorea globularis Morch, Beskriv. af Groenland., p. 96, 1857. 



Rhacostoma atlanticum Agassiz, L., Proc. Boston Soc. Nat. Hist., vol. 

 Ill, p. 342, 1850. 



Polycanna groenlandica Haeckel, Syst. der Medusen, p. 232, 1879. — 

 Whiteaves, Cat. Marine Invert. Eastern Canada, Publ. of Geol. 

 Survey Canada, p. 22, 1901. 



Zygodactyla groenlandica Agassiz, L., Contrib. Nat. Hist. U. S., vol. 4, 

 p. 360, 1862. — Agassiz, A., N. American Acalephae, p. 103, figs. 

 153-155, 1865.— Verrill, A. E., Rept. U. S. Comm. Fish and Fish- 

 eries, 1871-72, p. 729, pi. 37, fig. 275, 187 .— Fewkes, Bull. Mus. 



