MO U.S. NATIONAL MUSEUM BULLETIN 291 



and 4.84 ml/L. In the 4.45-4.59 ml/L group 23% of the tows took 28% 

 of the specimens while in the 4.60-4.84 ml/L group 24% of the tows 

 captured 24% of the individuals. A sudden drop-off occurs at concen- 

 trations higher than 4.85 ml/L; in the two increments 11.4%)" of the 

 total successful tows took only 2.8% of the sj^ecimens. Tows that were 

 taken at these concentrations were either in very shallow or very deep 

 w^ater, above and below^ the range of abundance of B. ahyssicola. The 

 peaks reflect in part, at least, the geographic positions of the captures. 

 The high O2 concentrations (above 4.70 ml/L) tend to come from the 

 Atlantic sector; middle values generally come from the eastern Pacific, 

 Drake Passage, and Peru Current region ; captures at low concentra- 

 tions come mostly from west of 120°W. Of course, values through the 

 whole range of concentrations may be found in nearly every area, but 

 they may not be at optimum depths or temperatures for B. abysslcola.. 

 The species is distributed primarily in low to medium Oo concentra- 

 tions (4.00 to 4.85 ml/L) in or below the O2 minimum layer in the 

 Antarctic, but Oo content is not the primary factor in governing the 

 distribution of B. ahyssicola^ because, where other factors are favorable 

 (e.g., temperature, depth, salinity), specimens have been taken in very 

 high or very low O2 concentrations. This is especially true in the 

 Atlantic sector of the Antarctic where the Oo concentration is high at 

 all depths. In other sectors of the Antarctic the very high O2 concentra- 

 tions are encountered only at relatively shallow depths; B. ahyssicola 

 has been taken occasionally at these depths where it is out of its normal 

 temperature range as well. 



The capture-plots on the vertical sections and the frequency distribu- 

 tions of oceanographic parameters together delineate the physico- 

 chemical conditions under which Bathyteuthis ahyssicola exists in the 

 Antarctic Ocean. 



Geographic Distribution in Relation to Water Masses 



An understanding of the three-dimensional distribution of pelagic 

 marine organisms requires the correlation of both horizontal plots 

 of geographic range and vertical plots of relationships of bathymetric 

 range with water masses. Ebeling (1962) has summarized previous 

 works that attempted to delimit animal distributions by the physico- 

 chemical and biological parameters of the environment. 



Very little has been done with the distributions of cephalopods, 

 particularly the oceanic forms. Bruun (1943) presented the geograph- 

 ical and vertical distribution of iSpinda spirula but made no attempt to 

 correlate distribution with parameters of water masses. In a later 

 work based on Galathea- material, Brunn (1955) reevaluated his previ- 

 ous decisions about the vertical range of S. spirula; he concluded that 



