SAGITTA GAZELLAE 2 5i 



for contraction can be seen, and in specimens having the hood fully extended (Fig. 12 a) the corona still 

 exhibits a sinuous outline. The corona of S. lyra shows no sinuous outline, yet the head of such a 

 similar species must be equally liable to muscular contraction. On the other hand, I have not found 

 a perfectly symmetrical corona in S. gazellae, but this structure in any specimen of any species is 

 seldom perfect, and the complexity of the 5. gazellae corona makes it difficult to speculate as to the 

 perfect outline. The features of the S. gazellae corona which serve to differentiate it from that of 

 S. lyra are the marked sinuosities between the eyes (Fig. \2a-d) (this portion of the corona often 



6) 



§ % * 



Fig. 9. Corona of S. lyra. 

 (From Tokioka, 1940.) 



Fig. 10. Variation in the shape of the 

 corona in S. lyra "gazellae" -type. 



Fig. 11. Corona of S. gazellae. 

 (From Ritter-Zahony, 191 1.) 



Fig. 12. Variation in the shape of the corona in S. gazellae. 



remaining when the rest is absent); the close proximity of the eyes to the corona; and the straight 

 cross-portion (Fig. 12 a, b, d) at the posterior end, which is quite different from the continuous curve 

 of the equivalent part in S. lyra. Although the difference in outline of the corona in the two species 

 may be considered a valuable taxonomic difference, it is not a very practical one, owing to the delicacy 

 of the structure and the consequent fact that it can so seldom be observed in specimens of S. gazellae. 

 Width between the eyes. This feature is perhaps the most convenient and precise of all. The width 

 between the eyes is given as a percentage of the width of the head. Table 9 gives the data from fifty 

 specimens of S. lyra "gazellae" -type and fifty specimens of the Subantarctic race of S. gazellae, to 



