90 DE. G. H. rOWLEE— BISCATAN PLANKTON : 



sufficient occasions (12), for inferences to be drawn as to its habits. Only small specimens 

 were captured ; the largest was about 5 mm. long, and many were less than 2 mm. 



DoLiOLTJM Kkohni, Hcrdman. 



Two gonozooids only of this species were taken, one in 21 b, one in 30 h, both in 100- 

 fathoni liauls. 



DoLiOLUM Nationalis, Borgert. 



One specimen in 30 I (50 fathoms) was apparently referable to this sj)ecies. 



DoLiOLTJM sp., Borgert. 



Dr. Borgert {op. cit.) records specimens from the hauls of the 'National' (coming, 

 with a single exception, " aus etwas grosseren Tiefen," many of them from the closing- 

 net), which showed a marked resemblance to Krohni, Herdman, as regarded the 

 formation of the gills and alimentary canal, but recalled varum, Gi'obben, in the form 

 of the generative organs. To this unnamed species may be referred two specimens from 

 36 I (350 to fathoms). On comparison with Krohni, the main differences recognizable 

 were of the character noted by Dr. Borgert : — 



DoHolum s]}., Borgert. Doliolum Krohni. 



Endostyle .... 1st iutcrmuscular space to 2iid intermuscular sioace to 



5th muscle. 4th intermuscular space. 



Gill-plate .... 4th to about 6th muscle. 5th muscle to Gth inter- 



muscular space. 



But he did not record, what was very noticeable in my specimens, the extreme thinness 

 of the muscle-bands, for they were as thin comparatively as in Natlotialis, far thinner 

 than in Krohni. The gill-slits were not exactly countable, owing to poor preservation, 

 but appeared to be about 16 to 20 in number. 



Being unable, in a single case, to find a ripening ovum in this unnamed form, Borgert 

 suggested as a possibility that the specimens were examples of Krohni which had failed 

 to reach sexual maturity (supposing them not to constitute a separate species) ; or, as 

 an alternative, that the differences between them and Krohni might be of a pathological 

 nature due to the deiith at which they lived. There is, of course, also a third possibility, 

 namely, that these forms are really Krohni which, dying before sexual maturity or after 

 sexual exhaustion, are sinking to the bottom, and that the differences in position of some 

 organs are attributable to post-mortem shrinkage and to distortion due to tow-net 

 pressure. Like Borgert, I failed to find ripening ova, the cells of the ovary seemed to 

 be all approximately equal in size ; but the whole appearance of this Ibrm is so different 

 from Krohni, its muscle-bauds are so thin, its test so slight, that I believe it to constitute 

 an undescribed mesoplanktonic species. My specimens are hardly good enough to allow 

 of a diagnostic description and figures. I suggest that it is a mesojilanktonic species, 

 not only from the ' National ' captures, but also from the distribution of the phorozooid 

 in the closing-net (p. 91). 



