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THE AMERICAN NATURALIST [Vol. XL VI I 



plankton of the sub-arctic, north temperate and tropical 

 Atlantic, the tropical Indo- Australian and the north 

 temperate Pacific oceans. S. gazella, on the other hand, 

 is a rare form. A few specimens were first taken during 

 the Gazelle expedition from the Indian Ocean (43° S.) 

 from a depth of 75 and 1,300 fathoms. It is also recorded 

 from the Atlantic Ocean (35°. 5 S.), where it was taken in 

 a single haul from about 1,400 fathoms, and from the 

 Antarctic Ocean between 60° and 66° S., where it was 

 taken from 10, 25 and 50 fathoms. These data indicate 

 that S. gazelles is confined to the southern hemisphere 

 and tends to be distributed circumpolarly. Records of 

 the Gauss expedition show that out of 88 hauls contain- 

 ing either S. lyra or 8. gazellce, 39 contained only the 

 former, 42 only the latter, and 7 both species. 



S. ENFL.ATA AND S. HEXAPTEEA 



S. en flat a is a warm water purely epiplanktonic 

 species whose northern and southern limits of distribu- 

 tion are 40° 24' N. and 34° 52' S. The highest tempera- 

 ture recorded in connection with its capture is 32° C. and 

 the lowest 15°.5 C. It has been taken from the north 

 temperate, tropical and south temperate Atlantic, the 

 south temperate and tropical Indo-Australian and the 

 north temperate Pacific oceans. 8. hexaptera, on the 

 other hand, is a eurythermal, nearly cosmopolitan species 

 found in the lower epiplankton or mesoplankton of the 

 arctic, sub-arctic, north temperate, tropical and south 

 temperate Atlantic, the south temperate and tropical 

 Indo-Australian and the north temperate and sub-ant- 

 arctic Pacific oceans. Its northern and southern limits 

 of distribution are 74° N. and 28° S., while the extremes 

 of temperature recorded in connection with its capture 

 are 29° C. and 6° C. 



Both species have been taken together from the same 

 areas during a number of expeditions. In the Siboga 

 area Fowler ('06) records 58 surface hauls containing 

 one or other of the species, of which 31 contained both, 



