4 ON A HARK BRITISH ENTOMOSTRACON. 



bristles. These setae, too, in mine are far longer than in the figures 

 given by Norman and Kurz. In Fig. 1 they are cut short by the 

 " inexorable limits of space." They should be continued in imagina- 

 tion about another inch, and the same remark applies to the post- 

 abdominal seta?, (f.) 



With regard to the first point of difference, I would suggest the 

 possibility, from the confusion which exists among them, of the setae 

 belonging to the branchial feet, which are plumose, having been 

 mistaken for the setne of the carapace, which in my specimens are not 

 plumose but branched. 



Kurz gives the measurement of the adult as : — Female, length 

 l-3Gin., height l-16iu., breadth l-34in. ; male, length l-61in., height 

 l-84in. Rather more than double the size of my specimen. 



The male (Plate I. Fig. 2, after Kurz) has the head larger in propor- 

 tion to the carapace than the female, and has a long bristle springing 

 from the front surface of the antennule. Its shape is not so spheroidal 

 as the female, for at the back, i.e., along the junction of the valves, the 

 carapace is flattened, almost concave. This, I opine, is because the 

 male has no need for an incubating chamber, since it has no eggs to 

 carry, and the space which in the female is provided for that purpose 

 is, in the male, reduced to a minimum. The male was found by Kurz 

 in August. 



The name Ilyoeryptus is derived from CKis, mud, and KpuTrrbs, 

 hidden ; sordidus means dirty. These epithets, though by no means 

 complimentary, are decidedly applicable to this species, for it is an 

 inveterate mud-lover, and is usually so covered with dirt, that it is 

 difficult to make out its internal structure ; so much so indeed that 

 Kurz gave up in despair the attonpt to delineate its branchial feet, 

 and omits them altogether from his figures ; whilst in the drawing 

 given by Norman they are represented by a few scratches of the pen. 

 Owing to mine being a very young and relatively transparent 

 specimen I was more fortunate in this respect, though I could only 

 see the fifth and fourth pairs distinctly, and must confess that the 

 three upper pairs are drawn as I think they are rather than as I saw 

 them. 



The motions of I. sordidus in the water are very curious. It keeps 

 up a succession of strokes with its antennae, which, however, only raise 

 it a short distance, and the weight of its body draws it down between 

 each stroke exactly as far as the previous stroke raised it. So the 

 animal is condemned to spend its whole life in a very limited area, ami 

 can never reach the surface of the water. 



Is not this, perhaps, the reason why the branchial feet are so large? 

 Theii i Eaoe must be oapable of producing a very strong current 



the valves; and it seems probable thai in order to secure an 

 equal amount of oxygenation to the blood, a slow moving species 

 urn more rapid branchial ourrent than a more locomotive 



one. Therefor. / iptus sordidus should have proportionately 



r br inchial i knia pulex. Which is the fact. 



