CHARYBDEA RASTONII. 19 



stalk. The lack of exumbral sculpture seems less important than Maas 

 supposed, since it was observed only on alcoholic specimens. Nor does 

 the condition of the phacellae appear to be sufficient ground for establish- 

 ing a new species, since the dendritic structure which he describes is not 

 essentially different from that of the phacellae of the half-grown C. rastonii 

 in the present collection, and Maas's specimens seem to have been at about 

 the same stage in development. Maas ('97) also believes that the sense 

 organs of C. arborifera show a marked deviation from those of C. rastonii, since 

 paired ocelli were present in all his specimens. But we know from Haacke 

 that it is only in individuals of the former species more than 20 mm. in 

 height ('87, p. 603, two thirds grown) that the paired ocelli disappear, and 

 it is by no means certain that the same may not be true of C. arborifera, inas- 

 much as the largest specimen which Maas examined was only some 15 mm. 

 high. Finally, the geographic distribution of these forms offers an additional 

 argument against regarding C. arborifera as separate from C. rastonii, since it 

 seems unlikely that two distinct, yet so closely allied, species should occur 

 side by side in such a restricted locality as Honolulu Harbor. 



For the sake of mapping out the distribution of the Medusa fauna of the 

 Pacific, it would be of great importance to know the true status of three 

 other species of Charybdea, jw/«//V)jma Semper, grandis Agassiz and Mayer, and 

 moseri Mayer, all of which are very closely allied in so far as regards the 

 structure of the phacellae and the number (24) of velar canals. Mayer (: 06) 

 believes that his new species C. moseri is very close to C.pMMpina. But it seems 

 to me that this is probably an error, since the two are sharply separated by 

 a constant difference in size, C. pliillipina having gonads when 30 mm. high, 

 while C. moseri shows no trace of them until some 60 mm. high. Charybdea 

 moseri and C. grandis, however, show such close affinities to each other that it 

 may be questioned whether they are not really two stages in the growth of 

 one species. Maas (: 03) has, it is true, suggested that C. grandis is in reality a 

 Tamoya, not a Charybdea. But Mayer's figures, though not altogether con- 

 clusive, indicate the short ilat manubrium characteristic of the latter genus. 

 There is no doubt of the correctness of Mayer's contention that C. moseri is a 

 typical Charybdea, a contention I have myself been able to substantiate on 

 a considerable series of well-preserved specimens from the Hawaiian Islands. 

 The only important difference between C. grandis and C. moseri is that in 

 C. grandis the twenty-four canals are slightly branched, whereas in all the 

 specimens of C. moseri they are simple. But since we now know that in 



