38 THE MEDUSAE. 



with growth the furrows become confined to the margin of the disc ; but in 

 species in which they occur they are still distinguishable even in the largest 

 specimens. Whether the number of the furrows can be regarded as of 

 specific importance is doubtful. All recent authors agree that when furrows 

 are present they are one less in number than the tentacles. Haeckel ('80), 

 however, described Collaspis achillis as having twice as many furrows as 

 tentacles. But considering the " suspicious circumstances " (Fewkes, '89 a , p. 

 531) under which this species was described, it is best, I think, not to lay any 

 stress on this character. The difference in form of the furrows, whether nar- 

 row or broad, the basis for the distinction of A. verrillii from A. wyvillei, is, ac- 

 cording to Yanhoffen, a constant one ; but, as we shall see, specimens in the 

 present collection present conditions which throw doubt on this conclusion. 

 Therefore it is best to reserve final judgment on this point until larger 

 series have been studied. 



Maas (: 03, : 04 c ) has described a hitherto unnoticed character in specimens 

 of A. valdiviae and A. bairdii, i. c. the presence of septal areas subdividing the 

 tentacular canals near their bases, the presence or absence of which may 

 prove, when more fully known, to be a specific character of great impor- 

 tance. Ground for this belief is afforded by the fact that these structures 

 are lacking in A. wyvillei, as well as in specimens from the Hawaiian Islands 

 described by Mayer (: 06) under the name A. alexandri. 



Whether the species which Yanhoffen and Maas recognize are all dis- 

 tinct, or whether such differences between them as the different sizes of the 

 septal nodes of A. bairdii and A. valdiviae are not, at least in part, due to dif- 

 ferent stages in growth or to individual variation seems to me very doubtful. 

 But it is hopeless to attempt any revision without large series of the 

 different forms. The following species seem to be the best founded, and 

 may be characterized thus : — 



Central disc fiat. With small septal nodes, A. bairdii Fewkes. With large 

 septal nodes, A. valdiviae Yanhoffen. 



Central disc, with radial furrows, lappets smooth. With narrow furrows, 

 A. verrillii Fewkes. With broad furrows, A. wyvillei Flaeckel. 



These may later prove to be synonymous, in winch case the earlier name, 

 A. wyvillei, must be retained. 



Central disc, with narrow radial furrows and marginal lappets with nettle 

 warts, 1 chum Vanhoffen, This species, since its discovery by the " Val- 

 divia bat been taken by the '-Scotia" (Browne : 08). 



