42 THE MEDUSAE. 



described species have a basis in fact. The features on which most of them 

 have been based — proportions of the bell, length of the mouth parts, 

 color, and form of the nematocyst papillae — were long ago shown by 

 Haeckel ('80) to be so variable as to make him doubt whether the various 

 forms are anything more than geographic races; but whether they deserve 

 even this rank is by no means certain, inasmuch as it appears that the 

 different types are not constant for different oceans. Thus, specimens with 

 a very short manubrium have been described from the European coast and 

 tropical Atlantic (P. perla Haeckel, '80 ; Maas, : 04 c ) ; from Bering Sea (P. 

 denticulata Brandt, '38), and from Zanzibar, the Philippine Islands, and the 

 coast of Peru (P. placenta Haeckel, '80, p. 510 ; Vanhoffen, '88, p. 12). A 

 like condition is also true of specimens with a long manubrium (P. pan- 

 opyra, P. cyanella) and for those with a manubrium of medium length. 



So variable, moreover, is this character, and also the form of the nettle 

 warts, even in a single swarm, that Vanhoffen (: 02 a ) found it impossible to 

 distinguish more than one species in the vast region, including both Atlantic 

 and Indian oceans, traversed by the " Valdivia." Fortunately Vanhoffen 

 (: 02 a , p. 36) has given us measurements of a very considerable series, — a 

 precaution neglected by most previous authors, — and from these I am able 

 to determine that the present specimens show no deviation from his, but 

 stand at about the middle of his series. Neither do they show any important 

 difference from his account in the form of the nettle capsules. From Mayer's 

 (: 06) figures this is evidently true also for specimens from the Hawaiian 

 Islands, and apparently also for the specimens recorded by Maas from 

 the collections of the " Siboga," and from Amboina. 



It appears, then, that one species of Pelagia occurs in the warmer re- 

 gions of the Pacific, Indian, and Atlantic oceans, — a conclusion easily recon- 

 ciled with its mode of development without any fixed stage, and in entire 

 harmony with the known distribution of such other oceanic Medusae as 

 Periph/jlla hyadnthina, Tthopalonema velatum, and Aglaura hemistoma, as well 

 as with the uniformity of the holoplanktonic fauna in general; but that it 

 is the only species of the genus in llicse regions is by no means certain. In 

 deciding what specific name to apply to this form, it seems to me best to 

 follow Maas (:03, : 06°) ami Mayer (: 06) in using the name of the earliest 

 described Pacific Bpecies, /'. /Htx'pi/nt I'eron, inasmuch as there is still reason 

 tu believe that the t\\<> Atlantic species /'. perla Slabber and P. noctiluca 

 l''i el Les. are specifically distinct. Maas (: 04°), who had previously 





