REVIEW OF GENUS ARGULUS MEEHEAN 491 



areas are composed of an oblong one anteriorly near the base of the 

 second maxillae and smaller than the other, which is some distance 

 posterior to it (fig. 30, a). The females measure to 8.5 mm. and the 

 males to 4 mm. The hosts are Lepidopsetta hilinmta and Cymato- 

 gaster aggregatus from Departure Bay, British Columbia. 



Figure 30. — Argulus borealis: a. Respiratory areas ; b, ribs of suction cups ; c, accessory 

 organs of second, third, and fourth legs. 



Suction cups with the rims supported by ribs composed of an 

 elongate rod and four to six overlapping plates (fig. 30, b). Mar- 

 ginal lappets delicate. Second maxillae with a wide basal plate, teeth 

 long and pointed ; postmaxillary spines also long. 



Antennae very trim; spines narrow, lateral hook sharp, anterior 

 knob slender, ventral median spine prominent, spines at the base of 

 the antennae and near midventral line long. Flagellum of first 

 antennae longer than the lateral hook; second antennae extending 

 almost to the edge of carapace. 



Thoracic appendages without flagella. The posterior surface of 

 the fourth appendage of the female with a somewhat bilobed fleshy 

 prolongation of the coxa. Second appendage of male with a slight 

 ventral posterior lobe (fig. 30, c). Third pair with an anterior 

 rounded swelling on the coxa and a broadening of the same segment 

 posteriorly where the socket is located. There is a posterior bilobed 

 natatory flap on the coxa of the fourth appendages; the basal seg- 

 ments of the appendage are short and broad, with a ridge around the 

 base of the peg on the distal anterior edge of the basis. The peg is 

 a large, round prominence near the base of the exopod with a con- 

 cavity around it. There is a bulbous papilla at the posterior end of 

 the thorax near the male opening. 



