. 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
. 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.
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