SEMAEOSTOME.E — PKLAGIA, CHRYSAOEA. 577 



(Esophagus shorter than in P. cyanella, only about one-quarter as long as bell-diameter. 

 Mouth-arms also much shorter, only about as long as bell-diameter. Nettling-warts upon 

 exumbrella larger and difterently arranged than in either P. cyatiella or P. phosphora; they 

 are concentrated near ape.\ of bell and not found near margin, elliptical in shape, sometimes 

 quite flat, or with a well-developed longitudinal comb-like ridge crossed by corrugations. 

 The largest warts are found at the apex of the exumbrella and they become smaller toward 

 the periphery. In the variety sublcvvis the bell is arched and more hemispherical than in 

 P. crassa. The gelatinous substance is thicker and the nettling-warts are larger and flatter 

 than in P. crassa. These forms are found in the middle of the tropical Atlantic between 

 Africa and South America. 



Genus CHRYSAORA P^ron and Lesueur, 1809. 



Chrysaora, Peron et Lesueur, 1809, Ann. Mus. Hist. Nat. Paris, tome 14, p. 364. — Eschscholtz, 1S29, Syst. der Acalephen, 

 p. 78. — Brandt, 1838, Mem. Acad, des Sci. St. Pctersbourg, Sci. Nat., ser. 6, tome 4, p. 384. — Haeckel, 1880, Syst. der 

 Meduscn, p. 510. — Claus, 18S3, Untersuch. Organisation und Entwick. Medusen, pp. 1-22. — von Lendenfeld, 1884, 

 Proc. Lin. Soc. New South Wales, vol. 9, p. 268. — Kishinouve, 1899, Zoolog. Anzeiger, Bd. ^^j P- 44-— Vanhoffen, 1888, 

 Bibliotheca Zoologica, Heft. 3, pp. 14, 22; 1906, Nordisches Plankton, Nr. 11, p. 47. — Hadzi, 1907, Arbeit. Zooi. Inst. 

 Univ. Wien, Bd. 17, p. 17, fign. 1-15, taf. 3, 4. — Heric, Ibid., p. 95, taf. 9. 



Chryiaora+ Melanaster, AoAsslz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, p. 162. 



The type species is C. mediterrunea Peron and Lesueur, of the Mediterranean. 



GENERIC CHARACTERS. 



Pelagidae with 8 marginal sense-organs, 24 tentacles (3 in each octant), and with 32 

 marginal lappets. 



The medusae of Dactylometra pass through a ^^ Chrysaora stage" in their development, 

 and there can be but little doubt that some of the so-called Chrysaora medusae are only im- 

 mature Dactylometra. The difficulty in distinguishing Chrysaora is still further complicated 

 by the very variable, individual coloration of these medusae, and by the fact that some species 

 ot Dactylometra, such as D. qmnqiiecirrha itself, become sexually mature in the Chrysaora 

 stage when living in brackish water. The Chrysaora and Dactylometra medusae are widely 

 distributed over the tropical and temperate seas and there are many local races. I believe 

 that future study will reduce the species to two or three, with numerous local varieties, as in 

 Pelagia or Cyaiiea. 



Chrysaora hysoscella ot the Mediterranean and Atlantic, and C. melanaster and C. helvola 

 of the North Pacific appear to be distinct species, while the other so-called species may be 

 varieties of the three above named or merely immature specimens oi Dactylometra. C. helvola 

 and C. melanaster finallv develop small, lateral lappets upon the sides of their 16 ocular lappets 

 and thus approach the Dactylometra condition in having 48 marginal lappets. The tentacles, 

 however, remain 24 (3 in each octant) as in Chrysaora. L. Agassiz proposes the generic 

 name Melanaster for Pelagidae with 48 lappets and 24 tentacles, but as this appears to be 

 but a transient stage in the process of growth oi Dactylometra, or a late stage in the devel- 

 opment of Chrysaora, we prefer not to adopt it. 



Chrysaora hysoscella, which is probably identical with C. mediterranea, is often hermaph- 

 roditic; young individuals being male, middle-aged ones hermaphroditic, and old ones 

 female. In other cases, however, the medusK are throughout life of one sex; while in others 

 male saccules develop among the old female gonads, and in other parts of the entodermal 

 layer of the subumbrella. 



The development of Chrysaora is through a sessile scyphostoma-stage, and the ephyra 

 is produced by polydiscus strobilization. The ephyra passes through an 8-tentacled stage 

 in which it recalls the condition seen in the adult of Pelagia. 



The mode of origin of the 4 primary stomach-pouches of the scyphostoma, and their 

 derivatives, has been the subject of a prolonged discussion between Claus and Goette, and 

 others. The view of Goette that the oesophagus of the scyphostoma is derived from invaginated 

 ectoderm received support from Hyde, and was generally accepted until 1907 when Hadzi and 

 also Heric (Arbeit. Zool. Inst. Wien, Bd. 17, Heft, i) made further studies of the development 

 of Chrysaora. It should also be remembered that R. P. Bigelow, 1 900, in his stud)- of the 

 development of Cassiopea is in accord with the views which were later put forth by Hadzi. 



