HYDKOMEDUSAE, SIPHONOPHORES, AND CTENOPHORES. 293 



Order LEPTOMEDUSAE. 



Family EUCOPIDAE Gegenbaur, 1856. 

 Genus PHIALUCIUM Maas 1905. 



I formerly defined this genus (proposed by Maas as a subgenus) 

 as " Eucopidae with numerous tentacles and otocysts (number inde- 

 terminate), with rudimentary as well as large tentacles; with or 

 without cirri " (1909a). Almost simultaneously Torrey (1909) sepa- 

 rated forms with cirri and instituted for them his new genus Phialop- 

 sis. This division has subsequently been adopted by both Mayer 

 (1910) and Vanhoffen (1911) and is followed here. 



Tables of the characters of the various described forms which fall 

 in Phialucium (sensu strictu) have recently been published by them. 



These authors agree in recognizing two well-defined species, caro- 

 linae and mbengha (Mayer lists both mbengha Agassiz and Mayer, 

 and virens Bigelow, but says that they are probably identical), and 

 I myself have maintained the same position (1909a). But Van- 

 hoffen separates the two species on quite different grounds from those 

 employed by Mayer or by me, and hence arrives at a different con- 

 clusion as to their relative geographic distribution. According to 

 Vanhoffen the two species are separated in the main by the number 

 of tentacles, mbengha having comparatively many, carolinae few; 

 and a second character is the number of otoliths to the otocyst, the 

 former having 5 to 6, the latter only 2. But if we examine the num- 

 ber of tentacles in the specimens which have been described, as given 

 in Vanhoffen's own table, adding thereto the present specimens, we 

 find that there is no discontinuity, but rather a continuous series. 

 The numbers in natural order of sequence are : 



Tentacles. 



Large. 



Rudi- 

 mentary. 



Total. 



Otocysts. 



virens Bigelow 



carolinae Mayer 



virens, Maas 



Philippine specimen 



mbengha Agassiz and Maye 



mbenoha Vanhoffen 



Do 



16-20 

 16 

 16 

 20 

 16 

 20 

 15 



30-40 



46-60 

 64 

 66 

 75 

 96 

 100 

 102 



(?) 



Phialidium tenue Browne was referred by me (1909a) to Phialu- 

 cium; Browne (1905), however, believes that it was an abnormal 

 Irenopsis. 



This table, I think, makes it evident that any division based either 

 on the number of tentacles as a whole, or on either class of tentacular 

 structures taken separately, would be purely arbitrary. 



