156 THE MEDUSAE. 



from the West Indies is so close that I have been unable to find a single 

 feature to separate them. 



The largest specimen measures 3.5 mm. in diameter ; but inasmuch as 

 this individual has several tentacles only partly developed, it is evident that 

 this is not the extreme size, but that Pacific like Atlantic specimens grow 

 much larger. The largest West Indian specimen is 5.5 mm. in diameter. 

 This is larger than any recorded by Mayer ; and the fact that the specimens 

 which he described were immature no doubt explains the few discrepancies 

 between his account and the West Indian specimens which I have studied. 



The bell is flat; seldom circular, but usually irregularly rectangular in 

 outline, from muscular contraction ; its cavity very shallow. 



Tentacles. — The largest number counted, in a specimen 2.5 mm. in 

 diameter, was thirty-nine, of which one was rudimentary. The smallest 

 number was twenty-four, one rudimentary ; the majority of specimens, 2 to 

 2.5 mm. in diameter, have from thirty to thirty-six tentacles, with from one 

 to four rudimentary. In a larger specimen from the West Indies, 3.5 mm. 

 in diameter, there are forty-six tentacles, and in another, of 3 mm., forty. 

 The tentacular bases form swollen, almost spherical bulbs, very sharply 

 separated from the slender distal portion of the tentacle, a characteristic 

 feature which is one excellent mark of the species (PL 38, fig. C). In con- 

 tracted specimens these bulbs are usually in close contact with one another ; 

 and even when the bell is expanded, though they are then separated by 

 considerable spaces, they are more crowded than in any other species of the 

 genus which 1 have studied. A similar form of the tentacles in Maas's (: 06 c , 

 pi. 2, fig. 7) figure suggests that his P. pacifica, from Amboina, is really not 

 the Oceania pacijica of Agassiz and Mayer ('99), but is more nearly related 

 to P. discoida, if not identical with it. 



Otocysts. — In both Pacific and West Indian specimens there is usually 

 only a single otocyst between every two tentacles. Mayer (: 00 b ), however, 

 has recorded from one to three otocysts between every pair of tentacles ; 

 but this discrepancy of observation is probably due to the fact that all of his 

 specimens were immature and that the final number of tentacles had not yet 

 dfvlnped. The number of otoliths in each otocyst varies from one to four; 

 ibly even more. Counting the otocysts is somewhat uncertain, because 

 of the crowded condition of the basal bulbs of the tentacles; and perhaps 

 in some cases there may be more otocysts than I have been able to find. 



Gon The large Bize of ihe gonads is a specific character of as much 



