598 TAGE SKOGSBERG 



this writer's work of 1874 b.) In a later work, 1890, ttiis investigator includes, besides this species, 

 two more species of this genus, H. pdagica and H. distincta. i)i these species C. Claus includes 

 only H. concha and E. felagica in his large monograph on this family, 1891 a. H. distincta, 

 the most important character of which was that its shell was furnished ,,mit zahlreichen runden, 

 im Centrum von je einem Porus durchbrochenen Gruben" (presumably, as G. W, MtJLLEH 

 pointed out, 1906 a, p. 50, not cavities, but calcareous concretions of an artificial nature), is 

 not mentioned at aU; C. ClAUS presumably discovered that it did not deserve the term ,distincta'. 



Different opinions have prevailed with regard to H. concha and H. pelagica. Many 

 investigators have taken them to be well differentiated species, e. g. 6. S. BkadY and A. M. 

 NoRAL\N, 1896, G. S. Brady, 1897 and V. VA\T!A, 1906. G. W. Muller, on the other hand, 

 grouped them together as one species in his work, 1906 a, and retained this view in his following 

 works. The only author who has clearly followed G. W. Muller in this question is Th. Scott, 

 1912 a; the other authors, A. ScOTT, 1905, P. T. Cleve, 1905 and Ch. Juday, 1906, have not 

 expressed any opinion in this matter; they apparently share, however, C. Claus's view. 



Which of these views is correct? As will be seen from the preceding I have followed that 

 of G. W. Mt'LLER. The reasons for this are as follows. According to C. Claus, one of the most 

 important differences between H. concha and H. pelagica is in the size of the shell. For the former 

 form this author gives a length of ,, circa 1,8 mm." (1891 a, p. 77), for the latter 1,1—1,4 mm. 

 (loc. cit. p. 78). The comparatively great constancy — pointed out above — in the lengths 

 of the shells in the great majority of the specimens of the form dealt with by me above 

 (cj = 1,4—1,6 mm., $ = 1,6 — 1,8 mm.) made me first inclined to think that this was really 

 a case of two separate forms, a larger and a smaller one. This view of mine was quite disturbed, 

 however, by my investigation of the small male caught at Station 116 of the Swedish 

 Antarctic Expedition. Although this specimen had a shell of only 0.95 mm. 

 long, it showed, curiously enough, on a particularly thorough and careful examination of all 

 the organs, a very far-reaching agreement in all respects with the other males investigated by 

 me. It seemed to be quite impossible to differentiate it as another species or variety. We are 

 thus probably concerned with a species with a very great amplitude of variation as to length 

 of shell. G. W. MilLLER, 1906 a, has brought forward a fact that supports this view: this investi- 

 gator points out in this work, p. 50, that at the same station he found numerous (28) males, 

 which showed, with regard to the lengths of their shells, all intermediate stages between 1,2 and 

 1,75 mm. 



The other differences adduced by C. ClauS must also be said to be of very little value. 

 They are partly characters which show a more or less continual variation. To this is added the 

 not inconsiderable uncertainty of C. Claus's descriptions. This is probably illustrated best 

 by the lack of agreement between the text and figures in this author's work — a contrast that 

 was already pointed out previously by G. W. MtJLLER, 1906 a, p. 50. As an example of this 

 G. W. MtJLLER points to the three end bristles on the sixth limb of H. pelagica in the work 

 mentioned. Other examples of this might also be given; I need only mention here the proportion 

 between the f- and g-bristles {?>- and a-bristles according to C. Claus's terminology) on the 

 endopodite of the second antenna in H. conclm and the number of the furcal claws in the males 



