12 COPEPODA 



had the opportunity of examining Kr0yer's original specimens of this species, I do not find it out 

 of place to add a few remarks. 



Kroyer's description and figure of Cal. Spitsbergensis apply without doubt to the mature 

 females; his description is clear and remarkably exhaustive; he has seen and described the receptacula 

 seminis ; his original specimen is a Cal. finmarchicus. Kr0yer's description and figure of Cal. 

 affinis applies to young specimens (St. V), but of his 3 original specimens the two belong to the 

 fourth stage. The description and figure of Cal. quinqueannulatus refer without doubt to the male 

 of Cal. finmarchicus ; Kroyer's original specimens were not preserved, but a number of specimens, 

 determined by Kr0yer as C. quinqueannulatus, were males of Cal. finmarchicus. 



As Kr0yer had unfortunately not examined mature specimens of Cal. hyperboreus, but only 

 young animals, he was obliged to establish his species on specimens of stage V; accordingly he did 

 not realise that the number of abdominal somites is not a systematic character, and was not able to 

 understand the full cyclus of development from nauplius to fullgrown animal of Calanus finmarchicus 

 cvi hyperboreus. He realised that is was too difficult for him to distinguish the earlier stages of these 

 two nearly related species. Starting from the stage V of Cal. hyperboreus he regarded the stage IV 

 as the oldest larve; he has given fairly good figures and clear descriptions of stage I IV; he has 

 recognised the nauplius and metanauplius as forming part of this cyclus. I think that Kr0yer was 

 the first to set forth the almost complete development of one of the Calanoid; so full a description of 

 several features does not seem to have been published for this species in spite of its importance (cf. 

 Dam as p. 8, who thinks that Gran is the first to recognise the larval stages). 



As I have been obliged to examine a big number of specimens of this species from the wide 

 area investigated by the Ingolf, the Thor and the East-Greenland Expedition, I have felt it necessary 

 to try to solve the question whether Sars is right or wrong in establishing the two species Calanus 

 finmarchicus and C. helgolandicus*}. According to Sars: 



The female of the more southern form C. helgolandicus is about 3 mm. long, the male 2'8 mm., 

 while C. finmarchicus is 4 and 3-6 mm. respectively; the former species is more narrow in form with 

 more angularly produced head. The urosome is in Cal. finmarchicus about half the length of the 

 metasome, and the caudal rami are somewhat longer than the anal somite, while Cal. helgolandicus 

 has the urosome exceeding half the length of the metasome and the caudal rami scarcely longer than 

 the anal segment In Cal. helgolandicus the antennulae extend only 2 segments beyond the caudal 

 rami but 3 in Cal. finmarchicus. The most important difference is found in the fifth pair of legs of 

 the male, which are more asymmetrical in Cal. helgolandicus with the Ri sin. extending a little beyond 

 the Re i (not beyond the middle of Re II) and with the Re III scarcely exceeding half the length of 

 the Re II (not nearly so long). 



The difference in size does not, as suggested by Sars, always correspond to a more northern or 

 southern distribution as pointed out by several authors. Mrazek (p. 502) has in the same samples from 

 Spitsbergen found mature females varying in size from 3-4 to 5-2 mm., Dam as and Koefoed have 

 from the same locality seen specimens varying from 3-2 to 5-4 mm. (cf. p. 382). Giesbrecht's spec- 



') A name, which Norman & Scott with good reason propose to replace with Cal. septentrionalis Goodsir. 



