403 



posterior aspect and separated from the outer portion by a 

 ridge marked with a number of short blunt teeth : the outer 

 branch forms* a flat plate, oval in shape, and bearing only one 

 plumose seta towards the inner side. In the second pleopod 

 (fig. 17) the inner branch is very long, ending acutely, its 

 basal portion is broad and not distinctly articulated to the 

 distal part ; on its anterior surface there is a groove, extend- 

 ing about half-way along the whole appendage and apparently 

 fitting against the inner portion of the endopod of the first 

 pleopod which closes the groove and forms the anterior wall 

 of the tube thus formed. The outer branch is irregularly 

 rhomboidal, having the outer margin fringed with a few 

 sparsely plumose hairs, the inner margin with a few small 

 short setae. 



In the ovigerous female the first pleopod (fig. 18) consists 

 of the outer branch only which forms a broad oblong plate 

 with rounded corners, as shown in fig 18 ; there is no sign 

 of the inner branch. The second pleopod (fig. 19) has the 

 outer branch slightly produced on the inner side, so as to be 

 rather more triangular, the inner and posterior margins bear- 

 ing a number of sparsely plumose setae ; the inner branch 

 is represented by a stout triangular process ending acutely, 

 indistinctly separated from the basal portion and much 

 shorter than the outer branch. 



The mouth-parts have been already partially figured by 

 Budde-Lund. They show a close general resemblance to those 

 of other species, e.g., D. acinosa, and do not call for a detailed 

 description. 



In D. marina, as in I), aucklandiae, the epimera 2, 3, 

 and 4 of the peraeon are separated from their respective seg- 

 ments by a fine but distinct sutural line, while in the male 

 they have completely coalesced with the segments. A similar 

 sexual difference is found in Ligia exotica and in some other 

 species. For further information on this point see my paper 

 on "Some Terrestrial Isopoda from the shore of Chilka Lake" 

 (1916, p. 465). 



From the description thus given it will be seen that D. 

 marina is closely allied to D. acinosa, from Cape Colony, the 

 pleopoda both of male and female being closely similar. It 

 can therefore stand with D. echinata, D. arniata, and D. 

 acinosa, in the subgenus Deto, Budde-Lund, as being some- 

 what distinct from D. aucklandiae and D. buccitlenta, which 

 form the subgenus Vinneta, Budde-Lund. The relationships 

 thus indicated agree well with the distribution of the species 

 and help us to understand how they arrived at the localities 

 where they now exist, the species of the subgenus Deto being 

 now found at Cape Colony, St. Paul Island in the Indian 



