244 DR. C. CHILTON ON THE SUBTEREANEAN 



gnathopods of these forms, which I consider immature males, are usually quite like 

 those of the ordinary female form ; but I have rough di'awings of one (made in 1883) in 

 which the j)ropodos of the first gnathopod is more ovate, the palm oblique, occupying 

 fully half the posterior margin, and the tufts of setae much reduced in number and 

 containing shorter setae or spines ; the second gnathopod has the carpus as usual, but 

 the propodos is shorter and differs in shape, being somewhat expanded distally, the 

 posterior margin bears only three tufts of setse instead of about eight as usual, and the 

 palm is rather oblique. It will be seen that in so far as this specimen differs from tlie 

 female it approaches towards the male ; I have, however, not succeeded in finding any 

 other forms intermediate between this and the fully-developed male. This particular 

 specimen presented a peculiarity in the third pair of uropoda, having the two rami very 

 unequal, one being as long as the peduncle and the other twice as long ; I have never 

 seen any other specimen with this peculiarity in such a marked degree, though specimens 

 are occasionally seen in which the two rami are a little unequal. 



In the first maxilla these " immature males " differ very considei*ably from the adult 

 form ; the ends of the paljis of the right and left maxilljB are quite symmetrical, and the 

 armature of the end of the outer lobe consists chiefly of broad comb-like setae like those 

 shown in fig. 18, PI. XXIII., being thus about as different as can be from the adult 

 form as shown in fig. 11, PI. XXII. In the former figure, only some of the setse are 

 shown, those on one side ; the other curved denticulated seta? which are found on the 

 other side and particularly towards the inner margin have been omitted in order to 

 show clearly those that are represented. I have found the first maxilla to be similar to 

 this in other small forms in which I could find no calceoli whatever, which were 

 jn'obably either still younger males or young females, and I suppose that this form of 

 the first maxilla is to be found only in immature individuals. Adult females have the 

 first maxilla practically the same as that of the large male represented in figs. 18, 19, 20, 

 21, PL XXIII., so far as the two palps and the armatui'e of the middle lobe are concerned. 

 I have not as yet found intermediate forms between the adult and the small specimens. 



Summary of the more important points in Part IV. 



It will be convenient here to summarize briefly the more important points that have 

 been brought out in the examination of the six species now described, as some of them 

 might otherwise be overlooked in the mass of technical description. 



(1) The genus Phreatoicus is shown to be a very peculiar one, requiring for its re- 

 ception the creation of a new family, the Plireatoicidoe, which approaches in some 

 respects to Asellidoe, differing, however, very much in the laterally-compressed body and 

 the long six-jointed j)leon. 



(2) The pleopoda of Phreatoicits are well-developed and in some respects different 

 from those of most other Isopoda. In the first pair there is a one-jointed endopodite 

 and a one-jointed exopodite ; in all the other pairs the exopodite is two-jointed, Avhile in 

 tlie third, fourth, and fifth pairs there is also a separate appendage arising from the 

 protopodite and probably representing the epipodite. In the male the second pair of 



