24 



As in the table of Zetesios, and for the same reason, namely the sharp contraction 

 lengthways of many specimens from deep water, the table is slightly irregular. 



Up to about 20 mm. the teeth were very much more numerous than in the Faeroe 

 Channel specimens. None of the specimens were in really good preservation, but so far as 

 could be ascertained there was no reason to doubt their specific identity with Moebius' species. 



14. Krohnia pacifica Aida. 



T. Aida. Op. cit., p. 19. 



L. Doncaster. Op. cit., p. 215. 



Characters. Head of medium size, neck fairly well marked; no collarette. Body 

 slender, but stouter than in subtilis, thickest about midway between septum and abdominal 

 ganglion, tapering gradually in both directions. Lateral fins beginning at nearly two thirds of 

 the distance from ganglion to septum, reaching posteriorly to the vesiculae seminales, generally 

 more on the tail than on the trunk, widest behind the septum. Tail fin rounded, extending 

 forward to the vesiculae seminales. Tail segment 25 to 41 per cent, of the total body-length, 

 generally less than in subtilis. 



Jaws with long acute tip ; they begin centrally on a gentle curve, with which the 

 straighter distal portion of the convex side almost makes an obtuse angle; at this point the 

 crest of the convex side is markedly thickened; the crest is thicker and darker in colour than 

 in subtilis. Teeth bayonet-shaped, springing from a thinner neck than is the case in subtilis, 

 more numerous than in subtilis of the same length. Corona ciliata short, clove-shaped, just 

 extending on to the head, but not reaching the eyes. No vestibular ridge observed. Formulae : — 



Siboga 



Ex.: 



9.0 



2 7 33 



8 



1 2 — 16 







8.0 



25—31 



8-9 



12 — 15 







7-5 



3>3 



8 



15 







7.0 



28 



8-9 



12—13 







6-5 



30 



6 



1 2 







6.0 



33—41 



6-9 



1 2 







5-o 



30 



8—9 



13 



Aida. 





6 



30 



9 



10 — 1 1 



Doncaster. 



7 



33 



9 



13 



The differences between this species and subtilis are very slight, but I must withdraw 

 the suggestion of their identity made in Biscayan Plankton (p. 79). At the same time the 

 characters set out above do not tally in every point with Aida's brief description; still, the 

 identity of jaws and teeth (the only magnified details which he figures), and the general 

 agreement, leave little room for doubt that we are both dealing with the same forms. He 

 describes the fins as lying equally on trunk and tail '), a condition which I have also noticed, 

 but generally more is distributed on the tail than on the trunk. 



1) His figure shows much more on the trunk than on the tail. 



