1908.] GEXUS OF AMPHIPOD CRUSTACEA. 393 



broad, and as long as the two following taken together ; 4th long 

 and very broad, laminarly expanded on both sides ; 5th half the 

 length of the 4th, ovate ; 6th narrow, much shoi'ter than the 4th ; 

 7th half the length of the 6th. 



SetiV. — The 3rd joint has one small seta on the posterior angle. 

 The 4th has six spines anteriorly inset along the chitinous margin 

 on the upper surface ; and, on the posterior margin, 14 or more 

 microscopic sensory setules set in little indentations. The 5th 

 carries one spine anterioily, and four (2 large and 2 small) on the 

 posterior angle ; the posterior margin has four of the minute 

 setules, and is thickly dentate along its distal half. The 6th and 

 7th as in the first peraeopod, the 7th having several minnte spines 

 on its upper surface. 



In the immature the 4th joint is expanded, about twice the 

 width of the succeeding joint. 



In the young (PI. XXI. fig. 1) the 4th joint is hardly longer 

 than the 5th, and not expanded ; the 6th is the second longest 

 joint of the perteopod. 



Setfe as in the first perasopod. 



Third Per^egpod. — Adult (PI. XXI. fig. 2). Second joint as 

 long as the three following taken together, laminarly expanded, 

 anterior margin lounded, posterior straight ; the posterior part 

 is produced downwards with its lower margin truncate. 3rd joint 

 very small ; 4th long, a little dilated posteriorly ; 5th and 6th 

 shorter than the 4th and much narrower ; 7th about two thirds 

 the length of the 6th. 



Setce. — The 2nd, 3rd, and 4th joints have each, at the anterior 

 angle, one strong spine ; the 4th also beai'S at intei'vals along the 

 anterior margin six small spines, and four laiger ones posteiiorly. 

 The 5th has one large one midway on the posterior margin, and 

 two at the anterior angle ; the whole of the anterior margin as 

 well as that of the 6th and 7th joints is strongly dentate, the 5th 

 and 6th each having two small spines inset. 



In the young (PI. XXI. fig. 3), the 2nd joint is not so long 

 nor so expanded as in the adult ; the 4th and 5th are subequal ; 

 the 6th and 7th are subequal and a little longer than the 

 preceding. 



Setce. — The 2nd, 3rd, 4th, and 5th joints each carry one seta 

 at the anterior angle ; the 6th has two at the posterior angle. 



Fourth Per^opod. — Adult (PI. XXI. fig. 4). The 2nd joint is 

 long, laminarly expanded, with both margins rounded ; the poste- 

 rior margin is produced downwards, lobate. The 4th is a little 

 dilated posteriorly, a little longer than the 5th and 6th which are 

 subequal ; the 7th is about two thirds the length of the 6th ; the 

 nail small and straight. 



Setce. — The 2nd joint is furnished at its anterior angle with 

 one large spine and seven long fine setaj extending beyond the 

 succeeding joint. These seta?, have each a slender shaft, with a 

 fine hair-like tip. Indented on the posterior margin ai'e five 

 very minute sensory setules. The 3rd joint has two spines ; the 



