BIGELOW: MEDUSAE AND SIPHONOPHOKAE. 383 



LEPTOMEDUSAE. 



Melicertidae Mayer. 



{Sensu em.) 



Cyclocanna, gen. nov. 



This new genus is proposed for a new leptomedusid, without otocysts 

 or other marginal sense-organs, but with two kinds of tentacles, large 

 and small, and in which the radial canals perform a peculiar S-like 

 curve, in their course from manubrium to margin. 



That this new Medusa belongs to the Leptomedusae is sufficiently 

 established by the location of the gonads on the radial canals (dis- 

 tinguishing it from the Anthomedusae), and by its hollow tentacles, 

 which separate it from all Trachomedusae except the aberrant fresh- 

 water Limnocnida. But its family relationship must remain more or 

 less doubtful until it is definitely known whether the absence of 

 otocysts (p. 385) is normal, or accidental. Under the former supposi- 

 tion, which is the more probable (p. 386), it must fall nearest the simply 

 organized Leptomedusae recently grouped by ^Nlayer (1910) under 

 Thaumantias,' being separated from the Laodiceidae (Browne, 1907) 

 by the absence of cordyli; from Melicertum by the number of canals; 

 and from the various other genera in which neither otocysts nor cordyli 

 are present, the Polyorchinae and Berenicinae of Mayer (1910), by 

 its simple canals. 



According to Mayer's 1,1910) scheme Cyclocanna would then fall 

 in the subfamily Melicertinae of his Thaumantidae. But there is a 

 serious objection to his system, in the fact that, being based wholly 

 on the simplicity, or style of branching, of the radial canals, it groups 

 together genera with, and genera without marginal cordyli, organs 

 which, as Browne (1907) has pointed out, are probably more signifi- 

 cant, phylogenetically, than is the precise character of the radial canals. 



Since the location of Cyclocanna in this general section of the 

 Leptomedusae depends on a character (absence of otocysts) yet to be 

 definitely established, it is useless to discuss the matter here, further 

 than to point out that if it actually lacks otocysts, it, together with the 



1 Poche (1914, p. 73) points out that the name can not be used in this sense because the type- 

 species T. hemispherica Eschscholtz 1829 was undoubtedly a Phialidium (Browne, 1896, p. 482; 

 Mayer, 1910, p. 198). 



