COPEPODS OP THE WOODS HOLE REGION 527 



Copepodid larva. — The metanauplius larva has no sooner emerged 

 from the egg than it molts into the first copepodid, or free-swim- 

 ming, form. The body in this form is much elongated and depressed ; 

 the head is elliptical and more than twice as long as wide, the pro- 

 portion being as 5 : 12. At about the center of each lateral margin 

 is a distinct sinus with a short dorsal groove extending toward the 

 midline but falling far short of it. This doubtless separates the 

 cephalic area from the rest of the head. Anteriorly the head is 

 narrowed and smoothly rounded, and the antennae, maxillae, and 

 maxillipeds extend prominently beyond its margins. Inside and 

 close to the frontal margin may be seen the mushroom tip of the 

 frontal filament, the stalk of which extends far back into the pos- 

 terior part of the head and is there coiled. The body behind the head 

 is made up of four segments, the first two thoracic and bearing the 

 swimming legs, the third the genital segment, and the fourth the ab- 

 domen bearing the caudal rami. 



The first antennae are 3-segmented, the basal segment longer than 

 either of the other two and armed with two setae on its outer mar- 

 gin; the second segment carries one outer seta, the third segment 

 seven marginal setae. The second antennae are biramose, the exo- 

 pod 1-segmented, globular and armed with three large setae, the 

 endopod 2-segmented, the end segment with a spine at each distal 

 corner and two smaller ones between them on the terminal margin. 

 The first maxillae are biramose, the exopod 1-segmented with a spine 

 on its outer margin, the endopod 2-segmented with three apical 

 spines. The second maxillae are 2-segmented with a long and slen- 

 der apical claw bent abruptly near its tip. The maxillipeds are 

 shorter than the second maxillae, but are 3-segmented, with a short 

 and nearly straight apical claw; the third segment carries a small 

 seta on its inner margin. 



Each swimming leg is made up of a basal portion which is 

 2-segmented and two 1-segmented rami; in the first legs the distal 

 basipod segment is much smaller than the proximal segment and 

 carries no outer seta, in the second legs it is fully as wide as the 

 proximal segment and has an outer seta. In the first legs the exopod 

 has two spines and four setae, the endopod has seven setae and no 

 spines. In the second legs also the exopod has two spines and four 

 setae, but the endopod has only five setae. Each caudal ramus car- 

 ries seven setae, of which two have their basal half enlarged into 

 flattened laminae, while the other five are slender and filiform. 

 Total length, 0.5-0.6 mm. 



Remarks. — This species is distinguished from Paeon ferox, which 

 it most resembles, by its much smaller size and by the relative lengths 

 of the ovisacs and posterior processes. In ferox these are about 



