342 DISCOVERY REPORTS 



a small papilliform process, whereas it is a large membranous plate, recalling the 

 exopod of the maxilla, in Upogebia (fig. 39). 



So far as I am aware this exite is found among Decapoda only in Euphausiacea, in 

 Caridina alone among Caridea, and in Anomura. In the latter it is large in Eupagunis 

 and very large indeed in Galathea and Porcellana. 



Whatever importance is allowed to the differences, it seems that the resemblances 

 have very much less weight. The only important characters are the presence of the 

 li7iea thalassinico, and the reduction of the gills. The former cannot have much signifi- 

 cance in Borradaile's opinion in view of its absence in Callianidea. It appears to be a 

 modification associated with breathing in burrows, and it is interesting to note the 

 observation of Pearse (191 1) on Thalassina that the sides of the carapace move on the 



Fig. 39. Maxillule of adult. 

 Upogebia stellata (a), and Callianassa truncata {b). 



hinge of this line as if panting for breath. The agreement in loss of epipods and podo- 

 branchs cannot be so readily dismissed; but the gill formula may vary so much as 

 between related genera that agreement is not a very sound basis to build upon. The 

 presence or absence of an appendix interna is a point of diff'erence of serious importance. 

 It is present in Axiidae and Callianassa and appears to be a feature of the ancestral 

 Decapod, though lost in Nephropsidea. 



While, then, the Upogebiinae and Callianassinae have a superficial similarity, there 

 is more ground, even on adult characters, for separating than for uniting them. In 

 view of the fundamental diff'erences in larval structure it is legitimate to assume that 

 they are not so closely related as has been supposed, and should be regarded as distinct 

 families. This conclusion is more or less in agreement with the table of relationship 

 given by Boas (1880, p. no); but the following scheme is, perhaps, a better expression 

 of the probabilities. 



