256 RECORDS OF THE AUSTKALIAN MUSEUM. 



wards but very rapidly near the tail septum ; tail segment rather 

 narrow, between sixteen and eighteen per cent, of total length of 

 animal ; anterior fins long and narrow, extending to about the 

 middle of the ventral ganglion ; posterior fin shorter and some- 

 what broader than the anterior, being widest at about the plane 

 of the tail septum, it does not reach vesicula seminalis ; tail fin 

 very deeply bilobed and not extending forwards to reach vesicula; 

 jaws nine, strong, most are well curved, youngest with very 

 strong base but nearly straight; anterior teeth six to twelve; 

 posterior seven to eleven ; vestibular ridge bearing short, 

 rounded papilla? and ending in a prominent process laterally ; 

 ridge shorter than posterior row of teeth. 



Its nearest allies appear to be S. bedoti, Beraneck, 13 S. furcala, 

 Steinhaus, 14 and S. sibogce, Fowler. 15 It differs from S. bedoti 

 in that the latter has a firm body, five to seven jaws, five to 

 thirteen anterior teeth and from ten to thirty-two posterior teeth, 

 a much longer tail segment (twenty-one to thirty-five per cent.), 

 and posterior fins reach the vesicular S. furcata differs from it 

 in the absence of a well marked neck ; in the position of the 

 widest part of the posterior fin, and in its greater length ; in the 

 distance between the two fins ; the number of jaws (six to nine) 

 and anterior teeth (three to eight). In S. sibogce, there are large 

 head ; short collarette ; firm, rather opaque body ; longer tail 

 segment (twenty-one to thirty-three per cent.) ; tail fin reaching 

 vesicula?; slender and comparatively straight jaws. In the above 

 comparisons, only the points of difference from S. australis have 

 been mentioned. 



I wish to express my indebtedness to Professor Haswell for 

 the loan of literature and specimens, and to Dr. C. H. Fowler's 

 Monograph of the Siboga Chaetognaths. 



Type presented to the Australian Museum. The sections are 

 the property of the Biology Department, Sydney University. 

 All drawings were made using a Zeiss camera lucida. 



II Beraueck — Rev. Suisse Zool., iii., 1895, p. 137. 

 14 Steinhaua — Loc. cit. 



« Fowler— " Siboga," loc. cit., p. 21. 



