25 



Aida states that "this species greatly resembles Krohnia subtilis, but is distinguished 

 by its small head, regular row of teeth, the smaller number of the teeth, and some other 

 characters". Grassi, it is true, emphasises the size of the head (in the text, though not in the 

 figure) but the camera lucida outline which I have given in Biscayan Plankton (fig. 50) shows 

 that subtilis has a medium rather than a large head; the neck in some markedly contracted 

 specimens makes the head look larger than it really is. As to the regularity of the rows of 

 teeth, this depends, both in subtilis and pacifica, on the amount of expansion of the head at 

 death ; the teeth may be spread out into a definite fan-like row, or (more usually) may be 

 compressed together so as to form the walls of part of a cone, the tips of the teeth converoino-. 

 As to the smaller number of teeth, pacifica actually has more than subtilis at the same total 

 length, but Aida's recorded specimen measured only 6 mm. 



Krohnia pacifica was also recorded by Doncaster from the Maldive Archipelago, 

 represented by two specimens reaching 7 mm. in length, one of which carried mature ova. 

 A 9 mm. specimen from Siboga Station 168, showed the same septate condition of the ovary 

 as Doncaster figured, there being six large ova on each side ; this septate condition is noticeable 

 in other species (e. g. Sibogae, serratodentata and ferox), and is apparently only an expression 

 of maturity, probably the only certain symptom of absolute female ripeness. 



15. Krohnia subtilis Grassi. 

 B. Grassi. Op. cit., p. 16. 



The great slenderness of the body, the high percentage value of the tail segment, the 

 character of the teeth and jaws serve to identify this with Grassi's species. The general 

 characters will be found in Biscayan Plankton (p. 78). 



Some points of distinction between this species and pacifica have already been mentioned. 

 In addition, the jaws of subtilis are thinner when viewed from the outer convex edge, and are 

 more transparent and lighter in colour. Both have much the same outline when viewed antero- 

 posteriorly, but the change of curve on the convex edge is hardly so abrupt as in pacifica ; and 

 at this point there is in subtilis a lesser thickening of the outer crest; on the other hand, the 

 inner concave border appears to be much thicker than in pacifica, so that the pulp-cavity 

 becomes very narrow. 



table shows four 



specimens 



only: 









13-5 



37 



? 



10 





1 2.0 



.37 



8-9 



? 10 





1 1.0 



45 



7-8 



9 



III. Genus Spadella (sensu Langerhans 1880). 



16. Spadella draco Krohn. 



A. Krohn. Op. cit., p. 273. 



B. Grassi. Op. cit., p. 15. 

 ? Spadella Vongai Beraneck. 



E. Beraneck. Op. cit., p. 155. 



SIBOGA-EXPED1TIE XXI. 



