488 



PROCEEDIISrGS OF THE NATIONAL MUSEUM 



VOL. 88 



openings are near two small rounded papillae, while the tactile 

 papillae of the female are short and stout. The whole under surface 

 of both sexes is very spinous. 



Antennae comparatively small; anterior hook very conspicuous, 

 flagellum very short; second antennae short; spines at base of first 

 and second antennae very stout, postantennal pair stouter, those on 

 ventral surface of lateral hook long and sharp. Suction cups on male 

 about one-fifth the width of carapace, ribs composed of basal pedestal 

 and 7 to 10 imbricate plates (fig. 28, c) ; those of female composed 

 of approximately 16 imbricate plates (fig. 28, d). Second maxillae 

 very stout and short, covered with armed padded areas; basal plate 

 broad with teeth blunt, anterior pair of postmaxillary spines short 

 and truncate, located on a large pad, posterior pair slender and blunt. 



Figure 2S. — Argnlus pugettensis : a, Male accessory organs of third and fourth legs; 

 b, respiratory areas; c, ribs of suction cups (male) ; d, ribs of suction cups (female). 



Swimming appendages bearing flagella ; boot-shaped natatory lobes 

 of fourth pair very stout on female. Precoxa of male elongated on 

 first three appendages ; basal segment of second appendages unusually 

 wide with a groove on the posterior surface, where it fits against the 

 next appendage. On the third appendage a thin-walled voluminous 

 sac extends the length of the coxa and part of the basis. Dorsally the 

 opening of the socket extends about two-thirds the length of the sac. 

 T]ie fourth appendage has a boot-shaped natatory lobe posteriorly, 

 and the usual chitinous ridge along the proximal side of the base of 

 the peg. The peg is odd in that it is composed of a triangular lamina 

 with the tip directed laterally and the base quite broad (fig. 28, a). 



This is the only species studied where the ribs on the rim of the 

 suction cups show any considerable sex differences. The female has 

 been reported up to 18 mm. and the male 8 mm. This large difference 



