REPORT ON THE COPEPODA. 35 



36° 9' S., long. 48° 22' W. (Station 324); lat. 36° 44' S., long. 46° 16' W., at a depth of 

 650 fathoms, from the dredge (Station 325). 



Although this species is certainly very nearly allied both to Calanus finmarchicus and 

 Calanus propinquus, I am unable, on account of the differences noted above, to refer it to 

 either of them. It does not seem likely that these differences depend upon immaturity, 

 seeing that the specimens appear to be of full size, and are perfect as to the number of joints 

 in the swimming feet, where, if at all, we ought to find signs of imperfect development. 

 Besides the two species here mentioned, Calanus tonsus might not unreasonably be 

 referred to several of Dana's species, notably to rotundatus, comptus, nuclus or magellanicus. 

 But in all these cases certain descriptive details given by Dana throw doubt upon the 

 propriety of such identification. Some of the points of divergence are these : — In 

 rotundatus the antennal setae are stated to be " short, those near the base scarcely longer 

 than the diameter;" in comptus the antennae are " a little longer than the cephalothorax ;" 

 in nudus the "abdomen is apparently three-jointed, yet the first articulation is somewhat 

 uncertain, antennae scarcely longer than the cephalothorax;" and in magellanicus there are 

 only " four pairs of natatories, the fifth rudimentary." 



5. Calanus gracilis, Dana (PI. V. figs. 1-6 ; and PI. XLVI. fig. 1). 



Calanus gracilis, Dana, Crust. U. S. Expl. Exped., p. 1078, pi. lxxiv. fig. 10. 



Length, l-7th of an inch (3*6 mm.). Anterior antennas about once and a-half the 

 length of the body, slender, sparingly clothed with very short setae, except the penultimate 

 and antepenultimate joints, each of which bears an excessively long, ringed, and densely 

 plumose seta. The outer branches of the third and fourth pairs of swimming feet in the 

 male have the margin of the last joint, between the base and the median spine, strongly 

 serrated (PI. V. fig. 5) ; in the female the same space is finely ciliated (fig. 4) ; the 

 terminal spines of the feet are simply sword-shaped, the serrations of the edge scarcely 

 perceptible : in the first foot, however, there is, as usual, no spine, but the outermost seta 

 of the external branch (PI. V. fig. 3, and PI. XLVI. fig. 1) is widened near the base, where it 

 forms a harpoon-like process, and the first joint is produced quite at the base into two 

 short, stout, divaricate spines, and has also a curious appendage, in shape somewhat like 

 the letter f slightly prominent, about half the length of the limb, and laid lengthwise 

 along its basal half. This is plainly seen without any dissection, and is quite diag- 

 nostic of the species. The fifth foot of the female does not differ from the rest, but 

 on the right side in the male (fig. 6) is of abnormal form, while that of the left side is 

 normal. The abdomen is short, scarcely one-third the length of the cephalothorax, 

 caudal stylets about as long as broad, setae short and subequal, except the second, which 

 is nearly as long as the whole body of the animal. All the setae of the swimming feet are 

 distinctly jointed in the middle. 



