14-0 



28 



13-5 



26 



i 3 .o 



26—30 



12.5 



3 2 



1 2.0 



25—33 



1 i-5 



33 



1 1.0 



27 



10.5 



29 



10. 



30 



Jaws short, strong, broad, strongly curved; the tips rather small. Both anterior and 

 posterior teeth as in ferox. 



Vestibular ridge with very slight undulations (unlike ferox). Corona ciliata of the same 

 type as in ferox, but not extending quite so far towards the ganglion. Formulae: — 



6 — 7 6 — 10 12 — 14 



7 5—6 11 



6—7 5—8 11— 15 



7 3 13 



5—7 6 — 8 11 — 14 



6—7 7 13 



7 6—7 n — 13 



7 7 1 1 — 1 2 



6 — 7 6 1 1 



The points of difference between ferox and robusta have been emphasised in the foregoing 

 characters rather than the points of similarity; the latter are also numerous and important, but 

 more conspicuous. 



It is possible that the specimens from Misaki which Aida attributed to hispida, Conant, 



were really referable to robusta, which had not been described at the time that Aida wrote. 



Robusta, Siboga Exp. 10 — 12 25 — 33 5 — 7 6 — 8 11 — 14 



Hispida Aida 11 25 7 — 8 7 — 8 11 — 17 



Hispida Conant 7 — 11 33 8 — 9 4 — 5 8 — 15 



At any rate it is apparent from the marked difference in the number of anterior teeth that they 

 were not hispida Conant: Aida further describes the head in his specimens as "comparatively 

 large", while a reference to Conant's figure of hispida shows a very small head. Aida's 

 description and figure agree sufficiently well with robusta, but I have only seen an eighth jaw 

 as a rudiment. 



10. Sagitta serratodentata Krohn. 



A. Krohn. Nachtragliche Bemerkungen iiber den Bau der Gattung Sagitta. Archiv fur 

 Naturgeschichte. Jahrgang XIX, p. 266. 



The characters of this widely distributed species have been given in Biscayan Plankton 

 (p. 58), and need not be repeated here. Such points of interest as were presented by the Siboga 

 specimens will be discussed below (pp. 29, 30) in connection with a more general question. 



The outline of a typical specimen (fig. 59) shows one or two slight differences from 

 the Biscayan type. Formulae : — 



14.0 28 7 9 — 10 18 



12.0 25 6 9 17 — 20 



1 1.5 26 6 9 18 



1 1.0 27 6 8 — 9 1 7 — 19 



