2 S 2 DISCOVERY REPORTS 



show the range of variation in the measurements. It can be seen that the average percentage for 

 S. lyra "gazellae" -type is double that of S. gazellae for the same state of contraction of the head and 

 the highest percentage for the latter species does not overlap the lowest percentage of the former. But 

 it will be seen from Table 9 that the range for each species is considerable, and this is due to the 

 position in which the head has been fixed. I have not found any overlap between the species; but it 

 is quite possible that in specimens with very distorted heads this may occur. Therefore, when using 

 this method, if specimens give a percentage between 30 and 40 the shape of the head should be noted ; 

 if the hooks are pointing in towards the mouth, and the hood is withdrawn, the head will be much 

 wider than normal, and the specimen will be S. lyra; if, on the other hand, the hood is forward, and 

 the hooks point straight forwards or outwards then the specimen is 5. gazellae. As a general rule, 

 however, specimens giving a percentage over 35 are S. lyra and under 35 are S. gazellae. 



Reference to Tokioka's (1940) illustration of S. lyra (" lyra" -type) 

 shows that the percentage of eye width to head width of the 

 specimen illustrated is 60, which fits the range of S. lyra given in 

 Table 9. Similarly, reference to Johnston & Taylor's (1921) illustra- 

 tion of one of the specimens which they describe as S. lyra shows 

 that the percentage of eye width to head width is 16-7, which is 

 within the observed range for S. gazellae given in Table 9. 



Mature stages. The appearance of the seminal vesicles and the 

 receptaculum seminis serves to distinguish between the species in 

 mature specimens only. The use of these differences is limited by the 

 fact that such specimens occur only at depths of 750 m. or more, and 

 are therefore not commonly taken. Both S. lyra (Ramoult and Rose, 

 1946 ; Ghirardelli, 1 950) and S. gazellae (see p. 270) breed in deep water. 



The seminal vesicles of S. gazellae occur midway between the 

 posterior and caudal fins, whereas Fraser (1952) states that in S. lyra 



they lie ' nearest the posterior fin '. Those of S. gazellae appear to differ slightly in shape from those 

 of S. lyra (Fig. 13), but are also of the ' enflata-type ' (Tokioka, 1939). Although I have examined 

 fairly large numbers of S. lyra in varying degrees of maturity I have found none with perfect 

 seminal vesicles, and must therefore depend upon published figures for comparison. 



The receptacula seminis are conspicuous white objects in S. lyra, but are not visible in S. gazellae. 



Two other features of difference in the mature animals may be noted. The number of hooks at these 

 stages in S. lyra is nearly always three on each side, whereas in S. gazellae there may be from three to 

 six (see Figs. 8 and 15). In 5. gazellae the posterior teeth are reduced to none, or occasionally one on 

 each side, whereas in fifty specimens of mature S. lyra I have never seen less than two, and usually 

 three on each side. 



Distribution. S. gazellae is confined to Antarctic and Subantarctic waters, whereas S. lyra is a 

 species with a world-wide distribution in tropical and subtropical waters, and is found in both 

 hemispheres. S. lyra has not been recorded from Arctic or Subarctic waters. Though Michael (191 1) 

 records S. lyra from very cold waters, he failed to differentiate it from S. maxima, and his table of 

 measurements of twenty specimens of S. lyra appears to contain a number of specimens of S. maxima 

 (nos. 1, 3, 5, 8, 11, 13, 14, 17, 18 and 19). On page 38 of his report he states 'it is possible that I may 

 have obtained both S. lyra and S. maxima and confused them ' ; I think it is just such confusion which 

 accounts for the records of S. lyra at very low temperatures, for Fraser (personal communication) 

 informs me that he has never observed S. lyra in Arctic or Subarctic waters. If S. gazellae is merely 

 a cold-water form of 5. lyra (as some authors maintain) which has colonized the Antarctic and Sub- 



Fig. 13. Seminal vesicle of 5. lyra. 

 (From Tokioka, 1940.) 



