NO. 5.] ACCOUNT OF THE SPECIES. 89 



apical spine of outer ramus in the 3 middle pairs rather slender, and slightly 

 incurved. Last pair of legs, as in Heterochceta, with a strong spine inside 

 the 2nd joint of the outer ramus; outer rami of the two legs in male not 

 very dissimilar in size and structure, though rather unlike those in female. 

 Length of adult female 4.82 mm. 



Remarks. This is a very conspicuous Calanoid, easily recognizable from 

 the other polar forms. Of the species recorded by Dr. Giesbrecht, A. longi- 

 caudatus (Glaus) seems to approach nearest to the polar species, at least as 

 regards the structure of the oral parts. It is, however, rather inferior in size, 

 and seems also to differ in some of the structural details. In any case, it 

 can hardly be supposed that the present species is identical with any of the 

 hitherto recorded species, all of which have quite a southern distribution. 



Description of the Female. 



The length of the body in adult specimens is 4'82 mm., and this form 

 is accordingly of rather large size, in this respect about equalling the Medi- 

 terranean species A. filigerus, Glaus, but considerably exceeding its nearest 

 ally, A. longicaudatus, the length of which is stated by Dr. Giesbrecht to 

 be only from 3'70 to 3'85 mm. 



The general form of the body (see PI. XXVI, figs. 1 & 2) somewhat 

 recalls that in Heterochceta norvegica, but is rather more slender. The 

 anterior division is but very slightly vaulted above (see fig. 2), and, seen 

 dorsally (fig. 1), exhibits a narrow oblong form, with the greatest width some- 

 what behind the middle, and not attaining even Vs of the length. The 

 anterior extremity appears narrowly rounded and somewhat abruptly con- 

 stricted behind, the posterior but very slightly emarginated in the middle. 

 The cephalic segment is well defined from the 1st pedigerous one, and not 

 quite as long as the remaining segments combined. It does not exhibit any 

 distinct cervical depression, and the front, seen laterally (fig. 2), is rather 

 narrow and angularly bent, projecting below in a small bifurcate rostrum, 

 which carries 2 delicate tentacular filaments (see PI. XXVII, fig. 1). The last 

 pedigerous segment is wholly coalesced with the preceding one, and has the 

 lateral corners evenly rounded off. 



The tail is rather slender, though not quite attaining half the length of 



the anterior division. It is only composed of 3 segments, the 1st of which, 



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