698 



MEDUS.E OF THE WORLD. 



Genus RHIZOSTOMA Cuvier, 1799, sens, restr. 



Rhizoslome, CUVIER, 1800, Bull, des Sci. Soc. Philomathique de Paris, tome 2, p. 69, planche 4. 



Rhizosloma, PERON ET LESUEUR, 1809, Annal du Museum Hist. Nat. Paris, tome 14, p. 362. ESCHSCHOLTZ, 1829, (in part), 



Syst. der Acal., p. 45. DE BLAINVILLE, 1834, Manuel d'Actinologie, Paris, p. 297. LESSON, 1843, Hist. Nat. Zooph. 



Acalephes, p. 411. GEGENBAUR, 1856, Zeit. fiir wissen. Zool., Bd. 8, p. 210. AGASSIZ, L., 1862, Cont. Nat. Hist. U. S., 



vol. 4, p. 150. 



Pilema, HAECKEL, 1880, Syst. der Medusen, p. 591. 

 Rhizostoma, CLAUS, 1883, Organisation und Entwick. Medusen, p. 60, Leipzig. VANHOFFEN, 1888, Bibliotheca Zoologica, Bd. I, 



Heft. 3, pp. 31, 43. MAAS, 1903, Scyphomedusen der Siboga Expedition, Monog. n, p. 80. 



The type species is Rhizostoma pulmo of the Mediterranean. 



GENERIC CHARACTERS. 



Rhizostomata scapulata with 16 scapulets upon the outer sides of the 8 mouth-arms. 

 The 8 mouth-arms are free, not fused together. Lower arms 3-winged, each terminating in 

 a single, club-like, gelatinous appendage. There are no other clubs, nor filaments among the 

 mouths. The 4 subgenital ostia are narrow cross-slits, each constricted by a wart-like papilla 

 upon the subumbrella. 16 radial canals, 8 rhopalar and 8 adradial, all of which extend to 

 the bell-margin. A network of anastomosing vessels arises from the outer halves of these 16 

 radial-canals, and this network gives rise centripetally to 16 blindly-ending areas in the 

 sectors between the radial-canals. There is no marginal ring-canal, but the most direct and 

 widest connection between the radial-canals is through the middle of the zone of anastomos- 

 ing vessels. 16 triangular areas of circular muscle-fibers alternate with the 16 radial-canals. 

 The marginal sense-clubs lack ocelli. There is an exumbrella pit above the sense-club and 

 the bortom of this depression is furrowed with radiating ridges. 



This genus is distinguished from Eupilema Haeckel by having 8 terminal clubs upon its 

 mouth-arms whereas these are absent in Eupilema. It is distinguished from Rhopilema by 



Synopsis of the varieties of Rhizostoma pulmo. 



