18 THE MEDUSAE. 



them are apparently branched, so that they present a tree-like appearance. 

 In the largest Hawaiian specimens each phacella consists of from six to eight 

 groups of filaments. 



The sense organs show the structure apparently universal at least among 

 the young of this genus, having two large single median and four small paired 

 lateral ocelli. But it is of course impossible to determine whether the paired 

 ocelli would be lost with growth, as Haacke ('87) found to be the case in his 

 Australian specimens. 



The Mangarevan as well as the Hawaiian specimens, agree closely with 

 Haacke's account of corresponding stages. Haacke ('87) and Mayer (: 06) 

 have described all the canals in the adult as branched, but the former author 

 has observed that in rather small specimens the eight canals next the sense 

 organs were entirely simple, while the eight next the tentacles showed only 

 a very faint trace of branching, a condition already attained in one quadrant 

 of our largest specimen. It is true that branching of the canals appears to 

 take place rather earlier in the Australian than in the Mangarevan specimens ; 

 but this slight difference, even if it prove to be constant, can hardly be con- 

 sidered anything more than a local peculiarity. 



The phacellae also closely agree with Haacke's account of corresponding 

 stages in their growth in his specimens. In the youngest which he exam- 

 ined they presented exactly the same condition as that which I have just 

 described for our smallest individual, the simple filaments of each phacella 

 arising in a single row from a thickening at the corner of the stomach. 

 The phacellae of our largest specimen resemble those of Haacke's half-grown 

 individuals, while in the large Hawaiian specimens they agree with his 

 account of the adult stage. There are no important differences between 

 our specimens and those described by Haacke other than such as may be 

 accounted for by different stages in growth. 



Since this species was first described by Haacke, the only record of its 

 occurrence is that given by Mayer (:06) from the Hawaiian Islands. The 

 identity of 0. arborifera Maas, which I have classed as a probable synonym of 

 this species, is not altogether clear. The strong general likeness of this form, 

 taken al the exacl locality, Honolulu Harbor, from which Mayer (: 00) has 

 .since recorded C. rastonii, to the latter species, has already been noted by 

 x l 97) himself. His specimens, however, showed two striking differ- 



ence, from the typical C. rastonii: the exumbrella was without sculpture; 

 and the phacellae weir dendritic, all the filaments of each arising from a single 



