19 



the trunk, reaching the vesiculae seminales. Tail fin rounded, making a more obtuse angle 

 with the tail than is usual in Sagitta. 



Jaws slender, not very strongly curved, and with small rather bUmt tips. Teeth broad 

 below, not very acute, the anterior as long as the posterior. 



Vestibular ridge with slight undulations. Corona entirely on the trunk, broad, of 

 medium length. 



The following table is based on eight specimens only : — 



4 6 



2 — ;, 6 



2 4 



2—3 5-6 



2 2 



In spite 01 its very small size, this is undoubtedly not the young of another species, 

 for instance neglecta : the extension of the ovaries to about midway between ganglion and head, 

 and the cap on the vesiculae seminales, showed that some specimens were not far from maturity. 



The chief differences between regularis and neglecta have been already discussed (p. 1 6). 



Doncaster's drawing of this species ' (Op. cit. fig. 7) which is very good as regards 

 the anterior end, seems to err, whcn compared with my specimens, in making the tail region 

 much too short (23 p. c. of total length without the tail fin, as against Aida's 33), and 

 consequently in placing too much of the posterior fin on the trunk. 



9. Sagitta robusta Doncaster. 



L. Doncaster. Op. cit., p. 212. 

 ? Sagitta hisplda Aida (non Conant). 

 T. Aida. Op. cit., p. 18. 



The close resemblance of this supposed species to ferox has already been discussed in 

 some detail (p. 10), and will be easily realised from a comparison (jf their descriptions and figures. 



Characters. General appearance between that oi ferox and that o{ serratodentata. 

 Head fairly large, jjroportionately larger than in serratodcntata, smaller than in ferox. In 

 expansion of the head, the neck is well marked, but almost disappears when the head is 

 contracted under the prepuce. There is a distinct collare'tte, slightly less both in breadth and 

 length than in ferox. Body proportionately slenderer than in ferox, but with very strong 

 longitudinal muscles and small lateral fields, somewhat less opaque than ferox, more so than 

 serratodcjitata. Trunk of nearly the same thickness from behind the neck up to just in front 

 of the tail septum, thence tapering gradually. Tail segment from 25 to 33 per cent. of the 

 total length. 



Anterior fins long, beginning at or just behind the abdominal ganglion, rounded, widest 

 a little before their posterior end and narrow-ing markedly forwards from that point (unlike 

 ferox), narrower and shorter than in ferox. Posterior fins larger than the anterior (unlike ferox), 

 rounded, more on the tail than on the trunk, widest behind the septum, reaching to the vesiculae 

 seminales when these are tumid. 



