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BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



or at some of the tentacles a second one may develop. When this takes 

 place it is at a very early stage, as in the Atlantic phosphorica. The 

 only record of specimens from the Indo- Pacific with paired otocysts' 

 prevailing is that by Maas (1905) . That is to say, we find here a ten- 

 dency, not completely effective, to retain permanently a condition 

 which is only evanescent in their Atlantic relatives. Or, in other 

 words, Indo-Pacific specimens show a tendency to advance in their 

 development to the degree of specialization exemplified by the At- 

 lantic form, but seldom attain it. On the other hand, there is no 

 record of the Indo-Pacific type from the Atlantic, though many 

 Atlantic specimens have been studied by various authors; most 

 recently by Neppi and Stiasny (1913). 



The singularis type is now known to be widely distributed over the 

 warmer parts of the central Indo-Pacific. In the Malaysian region 

 the phosphorica type also occurs (Maas, 1905), though it is not 

 recorded from elsewhere in that great oceanic division. 



The evidence is still too scanty to explain the meaning of this state 

 of things ; to tell how far the variation is hereditary, how far physio- 

 logical. Just such cases often meet the student of Medusae ; and they 

 offer constant difficulties in classification. 



Although singularis seldom, if ever, lacks paired otocysts entirely, 

 yet the two types, singularis and phosphorica approach discontinuity 

 because no true intermediates between an overwhelming preponder- 

 ance of one or other sort of otocyst, paired or single, are known. For 

 this reason, I have recognized singularis as a valid species; and it 

 is sufficient ground to do so still. But we must recognize that studies 

 of larger series may show that the two forms can not be so sharply 

 separated as the evidence now available suggests. Perhaps singularis 

 may finally be reduced to a variety of phosphorica. An open mind 

 is necessary if we are to mask neither the facts which we know, nor 

 the gaps which separate them. 



OLINDIAS SINGULARIS Browne. 



Olindias singularis Browne, 1904, p. 737, pi. 56, fig. 2; pi. 57, fig. 1. — 

 Bioelow, 1909a, p. 109, pi. 4, fig. 1 ; pi. 31, figs. 1-10 ; pi. 32, fig. 8. 



Olindias singularis — material examined. 



