68 COPEPODA 



a temperature between -f 0-49 C. and -f- 175 C. In the literature I was unable to find any further in- 

 formation about this species, but about M. pzisillus G. O. Sars, which possibly is identical with it, a 

 good deal of information is found. According to Far ran (1910 pp. 98 99) it has been recorded from 

 several of the Norwegian fjords at considerable depths, and from the sea between Jan Mayen and 

 Finmarken. According to Paulsen a species, which Sars has determined as M. pusillus, but which 

 really is M. pygmceus (cf. later on), occurred plentifully in a depth between 230 and 350 metres on the 

 north coast of Iceland ('4/ g 1904 662O L,. N. i2io L. W.). In addition it has been recorded from the 

 Irish Sea, the west coast of Ireland, the whole Norwegian Sea, the Skager Rak, the Kattegat and 

 in the extreme S. W. Baltic off Bornholm. 



At Spitsbergen (8oo2 L. N. I7O2 L. E.) it was found by the "Due d'Orleans" in a depth of from 

 60 30 m. (Temp. 0-40 0-27 C.) and by Hofsten and Bock (15040111. D.). 



The Belgian Antarctic as well as the National Antarctic Expedition has in the Antarctic Seas 

 collected a good number of a minute species by nets let down through holes in the ice to a depth 

 of 200500 met; they have been mentioned by Giesbrecht and Wolfenden respectively as 

 M. pygmceus and pusillus. The latter has pointed out that Giesbrecht's description refers to M. pu- 

 sillus (viz. comparatively short antennulae). Giesbrecht's localities lie between 7ii8 and 6g48 L,at. 

 South and 9222 and 8ii9 Long. W. If this identification is right, the species should certainly be found 

 in the deep sea all over the world. 



Remarks. I am fairly convinced, that the characters, which Sars has set forth to distinguish 

 Microcalanus pygmcsus and pusillus viz: shape of St. pes IV and length of the antennulae are not 

 sufficient. In this point of view I have been even more convinced by examing some specimens from 

 the North of Iceland, placed at my disposal by the kindness of Dr. Paulsen and determined by 

 Professor Sars as M, pusillus. Most of the specimens were young males with the anteunulae reaching 

 about to the middle of the abdomen; the spinulation of the St. of the natatory legs was not very 

 coarse. In a single specimen (lengt 0-84 mm.) the St. pes III has 16 dentations in proximal half in 

 contrast to Sars figure of M. pusillus with 10 teeth, and to an adult female from Ingolf St. 8 with 

 about 20. It seems evident to me that Paulsen's specimens ought to be referred to M. pyginccus, and 

 the fact that even such an authority as Sars has difficulty in distinguishing the two species from 

 each other, makes reservation necessary with regard to several identifications found in literature, and 

 bears out my doubts with regard to the validity of the two species. 



The partial value of the two main characters have been mentioned. According to Sars the 

 size of the adult specimens of M. pusillus scarcely exceeds 07 mm.; several of my specimens are 

 smaller. Mrazek, who has examined <$ and , varying in size from O'6o to 075 suggests the possibility 

 of referring them to two species, and Kraeeft points out minor differences between his specimens of 

 M. pusillus and Sars' decription. It may be admitted that a careful re-examination of a good material 

 from the different localities is necessary before settling the qustion of the identification of the species. 



12. Clausocalanus arcuiformis Dana. 

 (PI. I figs. 9 a d). 



1849. Clausocalanus arcuiformis n. sp. Dana. 

 1892. Dana. Giesbrecht, pp. 185 190, 



taf. I, 2, 10 and 36. 



1894. Clausocalanus arcuiformis Dana. Th. Scott, p. 73, pi. 8. 



1895. Giesbrecht p. 248. 



