On a S;peeies of Aearus. By A. D. Michael. 213 



and I most certainly have not ever seen or heard of one leg being 

 so developed without its fellow on the other side. It seems to me 

 that to find an analogy one must travel into a difi'erent order of 

 created beings; and that it is in the Crustacea and the single, 

 enlarged, copulative antenna of some of the Entomostraca that the 

 closest resemblance will be found. 



Another somewhat striking feature of the species is the extreme 

 massiveness of the chitinous strengthenings of the dermal skeleton ; 

 those round the anterior dorsal margin form a chitinous collar, 

 thickest between the insertions of the legs, and thinnest opposite to 

 them. The sternal and epimeral skeleton of the ventral surface, 

 particularly in the male, are also more powerful than I remember 

 in any other species. I have, however, remarked that the chitinous 

 strengthening is usually stronger in species parasitic upon aquatic, 

 and particularly marine birds, than in those found on terrestrial ones. 

 One is inclined to ask the reason of this, and the question is not 

 very easy to answer ; but I am inclined to think that the rougher 

 life led by the host, and the more constant exposure to alternations 

 of wet and drying, might be too much for the softer bodies of the 

 species found upon our sparrows and song-birds. 



Another characteristic of this species is the remarkable length 

 and size of the caudal projections in the male; it is somewhat 

 singular that the nearest approach to this, and to the general shape 

 of the present species, is in Dermaleichus starnse, a species found 

 by Professor Canestrini of Padua ; also on aquatic birds {Icarus 

 ridibundus, Starna fiuviatilis, &c.). 



I believe the species to be unrecorded, and if so, propose to call 

 it Heteropus. 



Description. 



Average length $ about 1 • 1 mm. 



» )> + J) ' '-' » 



„ breadth, both sexes, about '42 „ 



The lengths are measured from the centre of the posterior margin 

 of the body to the tip of the front outstretched tarsus. 



The colour of the skin, in both sexes, is the brownish white 

 usual amongst the Bermaleichi ; the skin is finely plicated into 

 folds on the ventral, and short, somewhat vermiform markings on 

 the dorsal, surface. 



The notogastral plate is somewhat chitinized, and light brown. 

 Masses of chitine which form the outer termination of the epimera 

 appear to lie on each side of each leg of the two front pairs, are 

 very dark brown, and, from their great development, are conspicuous 

 objects, the whole anterior margin of the creature, except the 

 rostrum, appearing to be strengthened by a great chitinous collar. 

 The legs are wholly chitinous. 



