z 4 8 DISCOVERY REPORTS 



Fins. An important feature of difference between the two species, and one which has not received 

 the attention it merits, is the position of the commencement of the anterior fins. This is appreciably 

 nearer the ventral ganglion in S. lyra " lyra" -type than in S. gazellae, but in 5. lyra "gazellae" -type 

 the lateral fields of the fins are often quite inconspicuous and thus the commencement of the fin is not 

 easily visible. In such a case the angle between the two nerve cords from the posterior end of the 

 ventral ganglion may be used as a guide, for the cords lead direct from the ganglion to the commence- 

 ment of the fin. Although this feature is most useful, it is one which requires experience of the species 

 to recognize with certainty and rapidity. 



a b c a b c 



Fig. 5. Fig. 6. Fig. 7. 



Fig. 5. Hooks from mature specimens of 5. gazellae and 5. lyra, traced from photomicrographs, (a) S. gazellae L.S. 85 mm. 

 long at stage III; first hook, (b) S. gazellae S.N. 62 mm. at stage III; first hook, (c) S. lyra 31 mm. at stage III; first hook. 

 Fig. 6. Mature specimens showing relative length at maturity and the shape and position of the fins and seminal vesicles. 

 (a) S. lyra at stage III. (b) S. gazellae S.N. at stage III. (c) S. gazellae L.S. at stage IV. 



Fig. 7. 5. lyra from its left side, showing the course of part of one of the ventral nerve cords across the lateral field between 

 the anterior and posterior fins. 



There are also several other points with regard to the position and shape of the fins. The appearance 

 of the junction between the anterior and posterior fins has been discussed by Tokioka (1939) and 

 Ghirardelli (1950); it is of no value in distinguishing S. lyra "gazellae "-type from S. gazellae. The 

 appearance of the posterior end of the anterior fin is much more sharply curved in S. lyra than in 

 S. gazellae (Fig. 6), but this is a difficult feature to see, and the delicate fins are often damaged. In 

 S. lyra "lyra"-type the lateral fields present a swollen appearance. Tokioka (1940) gives a good 



