64 ON A BAKE BRITISH ENTOMOSTRACON. 



mistaken for the setrn of the cai-apace, wliich in my specimens are )int 

 phimose hut hranched. 



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

 l-8(;in., height l-46in., hreadth l-34iu. ; male, length l-61in., height 

 I -8 tin. 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 hack, 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 lUinmjptus is derived from i\i/s, mud, and Kpinrrbs, 

 hidden ; xordidn^ 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 despaii' the attempt 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 foi'tunate in this respect, though I could only 

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

 three upper pairs are drawn as I t It in I; they are rather than as I saw 

 them. 



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

 up a succession of strokes with its antennas, 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, and 

 can never reach the surface of the wate)\ 



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

 Their great sui^face must be capable of producing a very strong current 

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

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

 must have a more rapid branchial current than a more locomotive 

 one. Therefore Ilijocnjptua .■iordidu.t should have proportionately 

 larger branchial feet than, say, Daphnia puJc.r. Wliich is the fact. 



The mere mud-loving propensities of the animal are not sufficient 

 to account for its dirty clothes. There must be something which 

 causes the dirt to adhere. According to Norman "it is probably in 

 consequence of these sluggisli liabits, and of the animal i-olling itself 

 in the mud, as well as owing to the pilose covering of the shell, tliat it 

 owes the coating of mud. Diatoms," A'c. The existence of the '• pilose 



