232 DR. C. CHILTON ON THE SUBTERRANEAN 



fine hairs and a small tuft of setse at the base of the dactylos. The dactylos is rather 

 short, and hears a single seta on the inner margin, imperfectly marking off the terminal 



unguis. 



The second percBopod is similar in all respects to the first. 



The tliird, fourth, and fifth perceopoda (see fig. 19) are all very long, and each is 

 longer than the preceding ; the fifth is about as long as the whole body. The lengths 

 of the perseopoda, as compared with the body, appear to vary, as is the ease also with 

 the antenmB, and to increase with the age and size of the animal. The coxae of these 

 peraeopoda are not easy to make out very distinctly ; that of the fifth is small, almost 

 semicircular, regularly curved below, and bearing four setse on the posterior portion ; 

 those of the third and fourth perseopoda appear similar, but flatter inferiorly, and with 

 fewer seta; ; that of the third fits in front into an emargination on the posterior side of 

 the coxa of the second pera?opod. 



It will be sufficient to describe the fourth perceopod (figs. 19, 20) as a mean between 

 the third and fifth. The basos is not much expanded, and narrows distally; both 

 margins bear small spines arranged in slight serrations ; the ischium bears one or two 

 spines at the extremity of the anterior margin ; the meros, carpus, and propodos are all 

 similar, but each is longer and narrower, and bears more numerous setse than the 

 preceding. In all both margins bear numerous tufts of long spines arranged in slight 

 serrations ; the dactylos is fairly long, of the same width throughout until near the end, 

 where it narrows suddenly ; at this point on the inner margin are usually three setae, 

 though in large specimens there may be as many as six. In the tuft of setae at the 

 base of the dactylos are stout spines, fine setse, and one or two plumose setae similar to 

 the " auditory setse " found on the antennae and elsewhere, but much curved or bent at 

 the middle. Similar setse are found in most of the tufts on the posterior margin of the 



propodos. 



The plcopoda are of the usual shape, and the three pairs are almost identical. Fig. 21 

 represents the third pair ; in it the peduncle appears to consist of a short coxa and a 

 long basos about three times as long as broad. The outer margin is somewhat convex, 

 inner margin straight and bearing four fairly long setse, the longest being at the 

 extremity near the two " coupliug-spiues." The latter seem to closely resemble those 

 of Gammarus neglectus, as described and figured by Sars [91, p. 53], except that there 

 are two only instead of three, as in that species ; each bears three or four teeth on each 



side. 



The outer ramus, which is somewhat shorter than the inner, is hollowed out on its 

 inner side for the reception of the base of the inner ramus, and its margin, which is 

 thinned out, bears four or five of the ordinary plumose hairs. The first joint of the 

 inner ramus bears on its inner margin three "cleft-spines," like those described by 

 Stebbing. 



The first and second pleopoda appear slightly larger than the third, and have the 

 spines on the inner margin of the peduncle smaller and fewer, otherwise they precisely 

 resemble the thu'd pleopoda. 



The first uropoda (fig. 22) extend as far backwards as the extremity of the second 



