244 G. M. Giles — Notes on the Ainpliipoda of Indian Waters. [No. 3, 



only. This was at last negatived by tlie discovery of egg-bearing 

 females belonging to both, species. 



The colouration of the two species is closely similar (although the 

 Atijlus has, if anything, a larger share of the bright yellow maculi on a 

 brown pnrphi ground that characterize both species) that I think that 

 there can be little doubt that we have to do with a case of mimicry, in 

 which case there can be little doubt that it is the Atylus who gains the 

 advantage, as the Amphithoe is much the stouter and stronger species, and 

 possesses the added advantage of being able to construct itself a home 

 which makes pursuit almost futile. Whether or not the Atylus avails 

 itself of deserted AmpJiitJioe nests, I am unable to say, as the resemblance 

 is so close that, until I had the whole catch under the microscope, I did 

 not suspect that I had to do with more than a single species. I am in- 

 clined to think, however, that such must be the case, as all my brightly 

 coloured specimens were certainly turned out of hiding places of sorts, 

 and so think that the probable advantage that is gained by the mimicry 

 is the facility of appropriating empty nests without being discovered as 

 a feeble interloper by the much better armed Amphithoe. It seems pos- 

 sible too that such a habit may be more or less a generic characteristic 

 of Atylus, as Liljeborg (Oefvers. Vetensk. Akad. Forhandl. p. 8, 

 1852) had already noticed a curious resemblance between Amphithoe 

 tenuicor^iis and Atylus compressus, though there is no note as to their 

 habits. 



The species, although a slenderer animal, is about the same length 

 (5 mm.) as Amphithoe incUca, and has the yellow maculi somewhat 

 larger and more regularly distributed than in that species. 



The head is proportionally larger and deeper, being nearly cylindri- 

 cal and much deeper than long. At its antero-inferior angle is carried a 

 black-pigmented compound eye much longer than the scarlet eye of the 

 Amphithoe. The cephalic shield is angulated in the middle line in front, 

 but can hardly be said to be rostrate. 



The thorax is small, forming considerably less than half the body 

 length and not much exceeding the abdomen in that respect. It is much 

 compressed, its segments being a good deal deeper than long, and its 

 posterior segments are, if anything, shorter than those in front. The 

 coxal plates are narrow, the anterior four being not more than half the 

 depth of their corresponding segments and the three posterior not much 

 more than a third the depth of the anterior coxee. 



The abdomen is large and deep, its three anterior segments being as 

 long as 1| thoracic segments ; the fourth segment is also of consider- 

 able size, equalling in length an average thoracic segment, and the last 

 two segments are very small. The telson is composed of two, quite 



