Boone, Coelenterata, Cruises of "Ara" and "Alva" 45 



Discalia medusina, Haeckel, E., loc. cit. A, p. 20 ; loc. cit. B, p. 46, 

 pi. 49, figs. 1-6. 



Porpita globosa, Schneider, K. C, Zool. Anz., Bd. XXI, 1898, p. 

 195, partim. 



Porpema prunella, Bigelow, H. B., Mem. Mus. Comp. Zool. vol. 

 XXVIII, 1911, p. 325, pis. 25, 26, 27, pi. 28, figs. 11, 15 (excel- 

 lent description, based on an extensive series of adult forms) . 



SCYPHOMEDUSAE 



Order: SEMAEOSTOMEAE 



Family: PELAGIDAE 



Genus: PELAGIA Peron and Lesueur 



Pelagia noctiluca (Forskal) 



■f 



Type : Forskal's type came from the Mediterranean Sea and 

 was deposited in the Copenhagen Museum. 



Distribution : This very beautiful medusa is pelagic in the 

 open seas of a very wide area of the Mediterranean and the warm 

 regions of the Atlantic Ocean. Curiously it is sometimes locally 

 abundant in the Mediterranean for several successive seasons and 

 then, without apparent cause, vanishes for several seasons. It 

 has been extensively studied at the Bay of Naples where it is espe- 

 cially abundant in summer but the larger specimens of it are 

 seldom recorded there in winter. 



Material examined: One young specimen, taken in 250 

 fathoms, off Fuerte Ventura, Canary Islands. 



Life History : The development of this species is most unusual, 

 being direct, without a sessile larval stage. It has been exhaus- 

 tively studied by Krohn (1855), Kovalevski (1873), Hamann 

 (1883), Goette (1893), Hyde (1894) and Mechnikov (1886). 



The structure of the gonads was examined critically by the two 

 Hertwigs (1878) and the development of the gonads by Hamann 

 (1883) . These organs first appear in the entoderm of the subum- 

 brella as four interradial, elongate ridges. The entoderm develops 



