COPEPODS OF THE WOODS HOLE REGION 19 



when the fifth legs are biramose, the number of segments given 

 are those of the rami alone, without including the basipods. But 

 when the fifth legs are uniramose it seems advisable to give the entire 

 number of segments in each leg, including the basipod segments, the 

 proximal of which is more or less fused with the same segment in the 

 other leg, and with the ventral surface of the fifth segment. The 

 statement that a pair of uniramose fifth legs is 1-segmented means 

 that there is but a single visible segment in the entire leg on either 

 side. Theoretically, we might assume, as Giesbrecht has done, that 

 in each leg there are 2 basipod segments, so fused with each other 

 and with the ramus of the leg as to be indistinguishable. The key, 

 however, is for the sole purpose of facilitating the recognition of the 

 various genera. It should include, therefore, only those things that 

 are actually visible and should present them as they really appear. 



The number of segments in the rami of the swimming legs is not 

 always constant for any given genus. In the genus Temora^ for 

 example, the exopods of the first 4 pairs of legs have normally 3 seg- 

 ments. But sometimes the separation of the two proximal segments 

 is so completely hidden that the ramus is apparently only 2-seg- 

 mented. Such genera, as far as seemed advisable, have been included 

 twice in the key, once as showing a ramus with 2 segments, and again 

 as showing one with 3 segments. Furthermore, the segmentation of 

 the swimming legs is not always the same in the two sexes of the 

 same genus. In such cases the sexes have necessarily been separated 

 and appear in different portions of the key. 



The normal habitat of each genus is also indicated, and is of value 

 chiefly in separating the genera that inhabit fresh, brackish, and 

 salt water. But it also serves to suggest what forms are likely to be 

 taken in surface towing and what forms are more or less confined to 

 the bottom plankton, with the depths at which they have been 

 obtained. 



Family CALANIDAE 



Genus CALANUS Leach, 1819 



Head either fused with the first segment or separated from it; 

 fourth and fifth segments separated ; urosome of female 4-segmented, 

 of male 5-segmented, symmetrical; caudal setae symmetrical, second 

 inner one the longest. First antennae usually longer than the body; 

 exopod of second antennae 7-segmented. Kami of all 5 pairs of legs 

 3-segmented, exopods with 1, 1, 2 outer spines and an end spine 

 shaped like a scalpel; first endopod with 1, 2, 6 setae, end segments 

 of second and third endopods with 8 setae, of fourth endopod with 5 

 setae. Fifth legs asymmetrical in male, the left leg the stronger. 

 Widely distributed and present in all the oceans. 



