PROBOSCIDACTYLA 219 



branching of the radial canals in the two species is very different, as has 

 been already pointed out by Browne (: 04). In P . flavidrrata the final niiin- 

 ber of canals and tentacles is very great (up to seventy-two) ; on tlie other 

 hand, in the present series, in sexually mature specimens, the maximum is 

 nineteen, and Maas (: 05, p. 21) has recorded a maximum of eighteen or more 

 for the " Siboga " specimens. In both mode of branching and number of 

 radial canals they closely resemble P. ornata McCrady, the common repre- 

 sentative of the genus on the Atlantic coast of North America, of which the 

 P. (jemmifera of Fewkes and of Mayer is beyond question merely the budding 

 stage. Maas, it is true, has maintained that a different location of the 

 medusa-bearing stolons separates Atlantic from Pacific species, they being 

 more proximal in the former, more distal in the latter, though in both occur- 

 ring either on stomach wall or canals ; but this character is variable in P. 

 ornata, while in the Pacific variety Huxley ('77) found them at the Jirsi, 

 Maas (: 05) at the second, branching of the radial canals. It seems to me, 

 therefore, that this character is of much less systematic importance than 

 the mode of branching of the canals, which, though more or less variable, 

 follows two fundamentally different types in P. ornata and P. flavidrrata. 



In studying the present series I was fortunate enough to have at hand 

 for comparison numerous specimens of P. ornata, and also one of A. Agassiz's 

 ('65) specimens of P . flavidrrata, which, in spite of its age, is still in fair con- 

 dition. The conclusion I have reached is that the present series is hardly 

 to be distinguished from P. ornata, except that the growth of the gonads 

 and the multiplication of the tentacles progresses rather further in the 

 Pacific than it normally does in the Atlantic species. I have been unable 

 to find a single characteristic, except that of budding, to separate it from 

 Haas's variety P. stolonifera. In type of brandling of the canals, number 

 of the tentacles, arrangement of the exumbral nettle ridges, form, and size 

 they are indistinguishable. I have, therefore, no hesitation in maintaining 

 that they both represent two stages in the life history of one form, which 

 is a variety of P. ornata, not of P. flavidrrata. It seems to me that the ques- 

 tion of geographic distribution has no force as an argument against this 

 conclusion, because, as Maas (: 05, p. 20) has pointed out, the occurrence of 

 budding practically puts this genus, like Cytaeis, in the same class with the 

 holoplanktonic forms in so far as its dispersal is concerned, and it is there- 

 fore in no way remarkable to find close allies in both the Atlantic and the 

 Pacific. 



