ON THE YOUNG OF THE ROBBER CRAB. 



589 



mandible. There is no palp. The first maxillae (Fig. 4) are much like those of Spiro- 

 pagurus. The second maxillae (fig. 5) bear six unusually distinct lobes. The three pairs 

 of maxillipeds show a strong resemblance to those of Eupagurus and Spii-opagui'us as 

 described by G. O. Sars (27). 



The upper and lower lips are also much like those of the above two genera. 



The jjaired eyes present that elongation of the crystalline cones of the hinder 

 half which is seen in other pagurines and in Thalassinidea (28). I was not able to 

 discover a " nauplius eye," but conclude that its absence is due to the state of 

 preservation of the specimens. 



Fig. 8. 

 Telson. 



If we now attempt to summarise in a few words the affinities of the zoaea of 

 Birgus, it may be said that the characteristics are those of the Anomalous Macrura 

 in general and of the Pagurinea in particular, that in most points it resembles Spiro- 

 pagurus rather than Eupagurus, but in the form of the telson inclines somewhat to 

 the latter genus, and lastly that its special peculiarity lies in an absence of spines and 

 teeth from parts of the body where they are found in allied forms and in a certain 

 simplicity of form throughout the whole organism. 



The first larva of the Robber Crab thus proving to be a very ordinary zoaea, it 

 would seem probable that the further course of development presents no unusual feature 

 till the final stages are reached in which the peculiar adult habitus is assumed. This 

 is a point on which information is still desirable, as also on the details of the period of 

 transition from a sea life to one on land. 



In ending, the writer must expre.ss his sense of the great obligation under which 

 Dr Willey has laid him by providing the material on which the above remarks are 

 based, consisting of a number of larvae and eggs and some valuable notes. 



78—2 



