14 G. O. Sars. 



its base, and acting upon the terminal part, the one con- 

 stituting the flexor, the other the extensor. The former is 

 much the stronger, consisting of numerous fibres converging 

 distally, and passing into a strong chitinous tendon, which 

 enter, the terminal part at the flexure between it and the 

 basal part, continuing almost to the tip of the former. The 

 extensor muscle, on the other hand, does not enter the 

 terminal part, but attaches itself at its base posteriorly. 

 The terminal part is about half as long as the 2nd basal 

 joint, and, as stated above, consists of 3 joints only, whereas 

 in the genus Diaptomus this part is distinctly 5-articulate. 

 It is highly chitinized and rather thick, being generally 

 doubled on the basal part; bat in the living animal it may 

 also admit of being stretched out so as to extend in a line 

 with the basal part. Just within the angle between the two a 

 small lobule is seen, carrying 2 unequal spines curved an- 

 teriorly; this lobule may, however, perhaps more properly 

 be referred to the basal part than to the terminal one. 

 The latter carries inside 2 slender curved spines issuing 

 from its 1st joint, and at the end is armed with 3 exceed- 

 ingly strong claw-like spines considerably exceeding that 

 part in length. On a closer examination, 2 of these spines 

 are found to originate from the end of the penultimate joint, 

 and the 3rd from the very small last joint. All 3 spines 

 lie in close approximation and are of about the same size, 

 being gently curved in their outer part, and finely den- 

 ticulated inside. 



Of the legs, as in most other Diaptomidæ, only the 4 

 anterior pairs are natatory, while the last pair are of a rather 

 diiferent structure, and not adapted for swimming. 



The natatory legs are comparatively short and densely 

 setiferous, the outer ramus carrying moreover strong 



