212 Transactions of the Society. 



V. — On a Species of Acarus, 'believed to he Unrecorded. 

 By A. D. Michael, F.L.S., F.R.M.S. 



{Bead 9th March, 1881.) 

 Plate IV. 



The singular creature which forms the subject of this paper belongs 

 to the genus Dermaleichus (Koch) Analges (Nitsch), but will not 

 fit into any of the five genera, or sub-genera, into which Eobin has 

 divided the group. I do not attempt to create a new genus or 

 sub-genus for it at present, because I think that our acquaintance 

 with the animals is too limited to make it desirable to attempt 

 exhaustive generic descriptions. 



I found several females, and one male, parasitic upon the cor- 

 morant, at the Land's End, Cornwall, in the autumn of 1879, but 

 this male presented such remarkable features that I feared it might 

 be a deformed specimen, and was afraid to describe it from a single 

 example. I could not obtain another, and therefore deferred 

 noticing the species until 1880. In the autumn of the latter year 

 I got some more cormorants, in the same place, and obtained more 

 males ; they were all ahke. 



The great leading feature, which is so striking in the male of 

 this species, and in which it is entirely different from every other 

 Acarus that I have seen, is, that the left leg of the second pair is 

 conspicuously larger than its fellow on the right side, has a totally 

 different tarsus, and is supported by a different and more powerful 

 epimeral * and sternal arrangement, so that the two sides of the 

 anterior half of the creatm-e are unequal. This occurs in the male 

 only, and I have no doubt that the enlarged leg is used for holding 

 the female during coition, although I have not been able to find a 

 pair in that act, as one usually may in most species of the genus. 



It is frequent, and even usual, among the Bermaleichi, for one 

 pair of legs, in the male, to be largely developed, for the purpose of 

 holding the female, and little, if at all, used at other times. The 

 enlarged pair of legs is generally the third, occasionally the first. I 

 am not aware that I have before seen the second pair so developed, 



EXPLANATION OF PLATE IV. 



Fig. 1. — Dermaleichus hetcropus, male x 95. 

 ,) 2. — „ „ female x 95. ' 



» 3, — „ „ under side showing the epimeral and sternal 



skeleton shaded dark, and exhibiting the 

 difference on the two sides. 

 )) 4. — „ „ one of the suckers highly magnified. 



* I use the word epimeron in deference to Professor Robin and M. Me'gnin, 

 who have employed it for the part spoken of. 



