SCYPHOMEDUSAE COLLECTED BY STEAMER " ALBATROSS." 187 



that of the other hydromedusae. Thus the umbrellalike bodies of 

 jellyfishes have probably been acquired in at least three different 

 ways within the group itself. Although nearly one-half of the known 

 forms of Scyphomedusae are confined to the Tropics, yet many of 

 these are rare, although, curiously, when found they usually appear 

 in swarms. Thus one may explore the Florida Eeef for 20 years and 

 not find a single Pelagia or Stomolophus, yet if an individual be 

 found there are almost certainly dozens or even thousands in the 

 neighborhood. It is as if they had all remained floating side by side 

 throughout their lives, or at least throughout the period when they 

 come to the surface from some well-defined region of the bottom 

 wherein they have spent their early days. 



Apart from the harbors and semibrackish estuaries one rarely finds 

 in the Tropics great swarms of medusae of a few species such as 

 characterize the coastal waters of the temperate regions. 



There are, however, exceptions to this rule, such as the enormous 

 number of Linuche, which when mature rise suddenly and simul- 

 taneously to the surface to cast out their genital products and then 

 to sink and die. For areas of square miles the tropical ocean is be- 

 sprinkled with these little brown thimbles, darting in a rapid jerking 

 movement. 



Similarly the pale milky Cubomedusae with their long pink tenta- 

 cles rise, when mature, from the depths to congregate along tropical 

 shores for the few days or weeks of the breeding season. 



Metschnikoff observed that many medusae cast out their eggs only 

 at certain definite times of the day or night. One of his Mediter- 

 ranean species, for example, laid its eggs always at about 3.30 o'clock 

 in the afternoon, and Conklin observed that Linuche casts its eggs 

 only at about 8 o'clock in the morning, but other Scyphomedusae are 

 not so regular, and indeed may retain the developing young in their 

 mouth folds for days or weeks before they escape into the ocean. 



DESCRIPTION OF GENERA AND SPECIES. 



Genus CARYBDEA Peron and Lesueur, 1809. 



Carybdea Peron and Lesueur, 1809, Ann. Mus. Hist. Nat., Paris, vol. 14, p. 

 332.— Mayer, 1910, Medusae of the World, vol. 3, p. 506. 



Generic Characters. — Carybdeidae, with 4 simple, interradial ten- 

 tacles and pedalia. Velarium supported by 4 bracket-like frenulae. 

 Velar canals present. Stomach small and 4-sided. 



CARYBDEA RASTONII Haacke. 



Carybdea rastonii Haacke, 1887, Jena, Zeitsch. fur Naturwissen, vol. 20, 

 p. 591, pi. 35, figs. 1-15.— Mayer, 1910, Medusae of the World, vol. 3, 

 p. 508. 



