ISOPODS OF NORTH AMERICA. 25 



fourth and is distally armed with a seta. The minute tubercle which 

 represents the flagcHum carries two setse. The whole antennae is 

 shorter than the flagellum in the first pair. 



'"''First gnatJiopodK. — These chelipeds are remarkable, both for the 

 threatening gape of the chela and for their length, which is double 

 that of the animars body. The second joint is the stoutest, yet not 

 much dilated, a little longer than broad. The third joint is short, 

 almost triangular. The fourth is of great length, narrowest near the 

 base, and nowhere very wide. The fifth is still longer, with a curva- 

 ture at its base, adapted for the folding together of these long slender 

 joints; its narrow inmiovable digit forms less than half of the total 

 length of the joint and ends in a sort of pointed claw over which three 

 setules are distributed, another setule occupying a small prominence 

 of the inner margin near the base of the claw. The movable finger 

 is somewhat longer than the immovable one, slender, pointed, curved, 

 with irregular margins. 



'"'' Second gnathopods. — As usual in this group, these are gnathopods 

 only in name, and differ but slightly from the following ambulatory 

 feet. They are scarcely, if at all, larger than the fifth peneopods, 

 having the second joint narrower, but the fourth and fifth joints a 

 little wider than is the case in that pair. 



'"'' Per xo pods. — The general structure is the same in all. The second 

 joint is the longest, in the last three pairs somewhat dilated. The 

 third joint is very short, the fifth joint is a little longer than the 

 fourth, and the sixth considerably longer than the fifth. There are 

 some spinules about the distal end of the sixth joint. In the first and 

 second pairs the finger is small, in the other three pairs it is nearly as 

 long as in the second gnathopod. 



'"'' Pleojpods. — All the five pairs are constructed as in Leptochelia. 



" Uropods. — The peduncles are a little longer than broad. The 

 inner branch has six joints, of which the first is the widest, the fourth 

 the longest. The outer branch has two joints, together not equaling 

 the length of the first joint of the inner branch. All the joints of the 

 branches are setiferous. 



'"''Length. — From head to tail the specimen measured less than a 

 tenth of an inch. From an unmounted specimen with which Mr. 

 Forrest has favored me since the above description was passed for 

 press, it appears that the lateral margins of the head anteriorly are 

 slight!}^ concave; that the first three free segments of the person are 

 very decidedly shorter and a little broader than the following three; 

 that, viewed dorsally, there is a constriction between the third and 

 fourth and between the fourth and fifth free segments, and that the first 

 five segments of the pleon are slightly broader than the immediately 

 preceding segments of the person. In both specimens the mouth 

 parts appear to be in a very rudimentary condition." — Stebbing.^' 



« Ann. Mag. Nat. Hist. (6) , XVII, 1896, pp. 49-56. 



