165 



So far as my knowledge goes, the division of tiae exopodite of 

 all the pleopoda except the first, into two distinct joints is very 

 unusual in the Isopoda: the plate attached to the outer margin 

 of the base (epipodite '■) also appears to be peculiar to this genus 



The Uropoda (Plate xxv., fig. 6) are well developed and extend 

 somewhat beyond the extremity of the pleon. The basal joint is 

 as long as the longer of the two I'ami and is very stout ; on the 

 under side near the base it bears two groups of stout setse, each 

 group containing about six or seven. The upper surface is broad 

 and slightly concave, each of the edges being supplied with a row 

 of stout spiniforra setfe, which are more numerous on the outer 

 than on the inner edge, and are largest towards the distal end. 

 At the end of the base below the articulation of the outer branch 

 are two very thick setse with a few pectinations at the end on the 

 upper side only. Many of the other stout sette on the uropoda 

 are pectinated in the same way though not to the same extent. 



The two rami are similar, subcylindrical in section, tapering 

 distally and curving slightly upwards. The inner is slightly the 

 longer, Vjoth bear stout sette and a larger number of fine setie or 

 hairs arranged in groups chiefly on the upper surface : the ends 

 of each are free from seta?. 



Sexual differences. — Of the specimens I have examined, nearly 

 two-thirds were undoubtedly males, all having the external male 

 organs present at the base of the seventh pair of thoracic legs. 

 One of these is shown in Plate xxvi., fig. G. The remainder of the 

 specimens were females. They are similar in general appearance 

 to the males but are slightly smaller, the subchelate hand of the first 

 pair of thoracic legs is less strongly developed, the fourth pair of 

 thoracic legs does not present the special modification found in 

 the male, and the second pair of pleopoda are of normal form. 

 None of the specimens examined bore eggs or young, but some 

 had what appeared to be small brood plates already developed on 

 the bases of the legs of the second, third and fourth segments of 

 the pereion. 



Position of Phreatoicus amoxg the Isopoda. 

 When I originally described the genus Phreatoicus in 1882 I 



in fig. 0. Besides these bodies I have found on other pleopoda great 

 numbers of other bodies which appear like empty spherical cases with a 

 small oblong or elliptical opening— many of them being bi'okeu or im- 

 perfect. I have not the least idea what they may be, but they are so 

 numerous on the pleopoda of some specimens that I thought it Vjest to 

 mention them. They ajipear merely to rest on the surface of the pleopoda 

 but whether their presence there is accidental or not I cannot say. A 

 small stalked Infusorian (Vorticella ?) is also found in great abundance 

 attached to the hairs of the pleopoda, three or four individuals usually 

 branching from the one stalk. 



B-July, 1891. 



