62 U.S. NATIONAL MUSEUM BULLETIN 291 



head lengths of all sizes of haoidifera lie within the range of points 

 for abyssicola (fig. 2). 



A comparison of the plots of head width against mantle length 

 shows that the head of small hacidifera may be slightly narrower than 

 that of abyssicola (fig. 3). In larger specimens the w^idths of the 

 heads of the two species converge. 



The lengths of the fins may differ in larger specimens of the two 

 species of Bathyteuthis. Only four specimens of hacidifera measure 

 between 19 and S7 nun ML; these have basal fin lengths that range up 

 to 20% greater than the basal fin lengths of abyssicola in the same size 

 range (fig. 4). The plot of fin width against mantle length for abyssi- 

 cola indicates that the fin width becomes more variable beyond a mantle 

 length of 30 mm (fig. 5) . The conxparable plot for bacidifera shows that 

 the two largest specimens (37 mm ML) and the specimen of 19 mm 

 ML have fin widths that lie near the upper limit of fin width for the 

 same size abyssicola. No significant difference is noted in the plot for 

 fin width vs. fin length (fig. 6) . 



Tentacle length is a difficult character to evaluate because the elastic 

 tentacles are subject to greater expansion and contraction during fixa- 

 tion than any other body part. A fair approximation of true tentacle 

 length, however, may be made w^hen a large number of specimens is 

 measured and plotted as in the case of abyssicola from the Antarctic. 

 When the plots for tentacle length vs. mantle length are compared, it 

 is noted that the tentacles of the few specimens of bacidifera tend to be 

 longer than the majority of abyssicola (fig. 7) . Specimens of bacidifera 

 12 mm in ML have tentacles about 30% longer than the tentacles of 

 abyssicola. At a mantle length of 37 mm the tentacle length of bacidi- 

 fera is about 18% greater than in abyssicola. 





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Figure 2. — Bathytevthis abyssicola, B. bacidifera: scatter diagram of mantle length vs. 



head length. 



