566 TAGE SKOGSBERG 



cases united under one species in the work in <|uestion, though these forms had been distinguished 

 by preceding writers as special species on account of greater or minor differences. 



Is this assumption of G. H. Fowl.EPv's correct? For several reasons it seems to me that 

 this f{uestion must be answered in the negative. 



Its uncertainty is shown by the very fact that it is based exchisively on a material collected 

 at a place so rich in closely-related species as the Bay of Biscay. An assumption of such a nature 

 must, in my opinion, have a more certain basis than that presented by G. H. Fowler. 



It would, of course, be desirable to prove or disprove this assumption directly by experi- 

 ments in aquaria. This was unfortunately, however, impossible for me because of the difficultv 

 of keeping these forms in full vigour for a long period of time in acjuaria. 



Another method of setting to work at this problem would be to investigate closely the 

 plankton material from districts which have few species of the genus Conchuecia and where 

 these species are comparatively distantly related to each other. Skager Rak is a district of this 

 kind. It is certain that there are only three species of this genus found here — at least regularlv 

 and to any large extent; this is shown with all the certainty that could be desired by the careful 

 investigations carried out by the .,Gonseil permanent international pour I'exploration de la mer". 

 These three species, C. elegans G. O. Sars, C. ohtusata G. 0. Sars and C. borealis G. 0. Sars, 

 represent three types of this genus that differ comjjaratively widely from each other. I have 

 had material from this region at my disposal. This material comprised (1) numerous mature 

 individuals and (2) larvae (of two or three different stages) of all these three species. On account 

 of the characteristic shape of the shell in these species the larval forms are very easy to distinguish 

 from each other with certainty. The fact that both larvae and mature individuals were found 

 of all these three species shows, of course, with complete certainty that we are concerned with 

 three different species and that none of them can be a ,, stage" of the other. It is certain that 

 the mature specimens all belonged to the same stage. The variations in size were strikingly 

 small: C. elegans: ^J = 2,05 — 2,25 mm.; $ = 2,0 — 2,15 mm.; C. ohtusata, ^ = 1,15 — 1.35 mm., 

 $=1,6—1,85 mm.; ('. borealis. (^ = 2,10—2.20 mm.. 9 = 2,5—2,7 mm. Other characters 

 were practically quite constant in these specimens. The same result was obtained by the 

 investigation of the material collected in February and that of August, a fact that is connected 

 with the phenomenon that the development of the H a 1 o c y p rids (like that of the C y p r i- 

 d i n i d s) takes place continuously during the whole year. (Among the mature females that 

 were investigated there were both old and young specimens; some of them had very small, 

 others more or less large, eggs.) 



I arrived at tlu^ same result after investigating the Halo c y p r i d s from the Arctic 

 and the Antarctic Oceans. 



It seems to be impossible to retain G. H. Fovnler's view under these circumstances. 

 Nor does it seem to me necessary to (;riticize in detail the exposition put forward by this writer; 

 I refrain from doing so all the more as such a criticism would necessarily be very lengthy, without 

 the result being of any great value. Only a few striking facts need be pointed out. 



In spite of obvious efforts ii. H. FoWLl'-H could not find two mature stages for more 

 tluui <'ii!lit (if the s])('ci('s invt'stigatt'd by him; utiIv (UU' mature stage was foiuid of thr other 



