No. 553] DISTRIBUTION OF THE CHJ-JTOGX AT1IA 27 



while 26 contained S. enflata but not S. hexaptera, and 

 only one contained 8. hexaptera alone. During the first 

 expedition of the Pola to the Eed Sea 32 surface hauls 

 were made which contained both species, 21 which con- 

 tained 8. enflata but not S. hexaptera, and only one 

 which contained S. hexaptera alone. During the second 

 expedition not a single 8. hexaptera was taken in surface 

 hauls that was not accompanied by S. enflata, there being 

 13 hauls containing both and 29 containing S. enflata 

 alone. Finally, during several expeditions covering 

 parts of the Adriatic, Ionian and yEgean seas, Ritter- 

 Zahony ( '08) records 45 surface hauls containing S. en- 

 flata, of which 6 also contained 8. hexaptera, and only 4 

 hauls in which the latter species was taken without the 

 former. 



These data certainly indicate a high degree of coinci- 

 dence. However, the fact that S. enflata is rarely re- 

 ported other than from the upper epiplankton and that 

 8. hexaptera is more typical of the lower epiplankton and 

 mesoplankton, suggests isolation with respect to sex- 

 ual maturity. Concerning this Ritter-Zahony ('10 6), 

 who has been very careful to distinguish immature from 

 mature specimens, says: "Like S. serratodentata, S. 

 hexaptera is a species which can not endure low tempera- 

 tures until it has reached the adult stage. . . . We do 

 not, as a rule, find large specimens until we come to the 

 lower epiplankton." Until more is known regarding the 

 stages of growth of these specimens taken on the surface 

 together with S. enflata we can not regard the cases of 

 coincidence revealed above as anything more than nega- 

 tive evidence of isolation. 



S. PLAXKTOXIS AND S. FEROX 



8. planktonis is a eurythermal species recorded from 

 both epi- and meso-plankton of the north temperate At- 

 lantic and Pacific oceans. It has not been reported north 

 of 32° 45' N., nor south of 8° 30' S., except for a few 

 small specimens from the Antarctic between 65° and 



