EPERETMUS, A NEW GENUS OF TRAOHOMEDUSAE. 



By Henry B. Bigelow. 



Of the Miiseum of Comparative Zoology, Cavihridge, Massachusetts. 



Among a miscellaneous collection of Medusae loaned me for study 

 by the United States National Museum is a specimen wliicli I at first 

 took for an Olindias, but which proves, on closer examination, to rep- 

 resent an undescribed, though related, genus. 



In previous papers (1909, 1912, 1913) I have followed Browne 

 (1904) and Maas (1905) in using the family name Petasidae for the 

 assemblage of closely related genera, whose best-known members are 

 Gonionemus and Olindias. But with the passage of time it becomes 

 less and less likely that Haeckel's (1879) genus Petasus (on which the 

 family name Petasidae is based) will ever be connected with any actual 

 Medusa; hence it is increasingly probable that the name Petasidae 

 \^'ill have to be abandoned to be replaced by Olindiidae (sensu Browne, 

 1905). Browne and I have divided the family into two subfamilies, 

 Ohndiinae and Petasinae, the former for genera in which the otocyst 

 clubs are inclosed in a capsule (which, itseK, may either stand free on 

 the beU margin or lie inclosed in the gelatinous substance of the 

 exumbrella or velum), or stand free on the bell margin. Mayer (1910) 

 and Goto (1903) have used a different criterion, namely, the presence 

 or absence of tentacular suckers, resulting in a totally different align- 

 ment of genera. But throughout the medusan series the structure of 

 otocyst is much more significant than of tentacle. And that their 

 system is the more artificial of the two, neither of whichcan, perhaps, 

 claim to be a truly natural one, is shown by the fact that it throws into 

 different subfamihes genera as closely related as Gossea and Gonione- 

 mus. Up to 1912 the subfamily Petasinae, as defined by Browne and 

 me, contained only Haeckel's apocryphal genera Petasus, Dipetasu^, 

 Petasata, and Petachnum, none of which have been seen since first 

 described. But in that year a new genus, Nauarchus, was added to 

 the list, thanks to its free otocyst clubs (Bigelow, 1912). All the other 

 genera belong to the Olindiinae. 



The various Olindiinae are obviously closely related to one another, 

 but the characters which separate them are remarkably precise for a 



Proceedings U. S. National Museum, Vol. 49— No. 2114. 



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