324 



MEDUSA OF THE WORLD. 



y'oung medusa. — In the youngest medusa observed the bell was about 5 mm. in height 

 and about twice as high as it was broad. There were only 4 radial tubes. There were 8 long 



tentacles with conical, hollow, basal 

 bulbs and about 16 slender cirri. 

 In addition to these there were about 

 12 lithocysts each containing 2 to 3 

 concretions. As development pro- 

 ceeds the bell becomes relatively flat- 

 ter. The radial tubes increase in 

 number, so that specimens of 25 

 mm. diameter have about 12 canals. 

 The periphery of the stomach in 

 these young medusae is irregular in 

 shape, but when the animal is about 

 50 to 60 mm. in diameter it becomes 

 cross-shaped, the radial tubes arising 

 from the ends of the arms of the 

 cross. At about this time the genital 

 organs develop upon the radial- 

 canals. New radial tubes arise from 

 the periphery of the stomach and 

 extend downward toward the circu- 

 lar vessel. 



This rare medusa is occasionally 

 found along the New England coast 

 from Massachusetts Bay to Grand 

 Manan, from July until September. 



'f 



Figs. 183 and li^.—Halopsis ocellata, after A. Agassiz, in North Ameri- 

 can Acalephae. 183, oral view; 184, bell-margin. 



Genus jEQUOREA Peron and Lesueur, 1809. 



Medusa icquorea, Forskal, 1775, Descript. animalium, p. no; 1776, Icones rerum natural., plate 32. 



/Equorea, Peron et Lesueur, 1809, Ann. Mus. Hist. Nat., tome 14, p. 336— Lamarck, 1816, Hist. Nat. Anim. sans Vert., tome 2, 



p. 498. 

 Mquorea-v Mesonema, Eschscholtz, 1829, Syst. der Acalephen, pp. 108, 112. — Maas, 1905, Craspedoten Medusen der SAoga 



Exped., Monog. 10, pp. 40, 42. 

 Mquorea+Crcmatostoma + Mesonema+Rliegmaiodes + Rhacostoma, Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 359-361. 

 /£quorea+ Rhegmalodes+ Mesonema+ Polycanna, Haeckel, 1879, Syst. der Medusen, pp. 218, 221, 225, 229. 

 /Equorea, Claus, 1881, Arbeit. Zool. Inst'. Wien, Bd. 3, p. 283; 1883, Untersuch. iiber Organisation und Entwick. der Medusen, 



p. 80.— Browne, 1903, Bergens Museums Aarbog, No. 4, p. 20. — Bigelow, 1909, Mem. Mus. Comp. Zool. at Harvard 



College, vol. 37, p. 170. 

 Zygodactyla (Campanula a) (hydroid), Hincks, 1868, Hist. British Hydroid Zooph., p. 191, plate 38, fig. 2. 

 Phorcynia, Oken, 1815, Lehrbuch der Naturgesch., Theil 3, p. 121. 



The type species is the highly variable /Equorea forskalea Peron et Lesueur, 1809, of 

 the Mediterranean and Atlantic. 



GENERIC CHARACTERS. 



^Equorida; with more than 8 simple, unbranched radial-canals which arise separately 

 from the margin of the stomach and with more than 4 lips. Subumbrella smooth, without 

 wart-like protuberances. Tentacles, lithocysts, and excretion papillae numerous. Hydroid is 

 Campanuhna. 



This genus is closely allied to Zygodactyla, but the surface of its subumbrella is smooth, 

 whereas in Zygodactyla it is covered with interradial radiating lines of wart-like gelatinous 

 papillae which alternate in position with the radial-canals. 



The lithocysts in /Equorea are closed vesicles on the subumbrella margin of the velum, and 

 the concretions are of ectodermal origin. A conical excretion pore is commonly found on the 

 inner (subumbrella) side of each tentacle-bulb adjacent to the ring-canal. Ocelli are unknown. 



Medusas of /Equorea commonly display great individual color variability, ranging through 

 deep-blue, violet, milky, or transparent, and in their ontogeny they are also quite variable 



