146 CRUSTACEA. 



as thus characterized, is widely different from Eudora of De Haan, 

 although both include the same species as type; for Eudora is so 

 described and used by its author, as to embrace, also, other species 

 having the orbit of Xantho. 



The importance of making the ridge bounding the efferent passage 

 a distinguishing family characteristic, instead of mere form or width 

 of carapax, is abundantly illustrated among the species. From Xantho, 

 the transition, in general form and other characters, is very gradual 

 to Xanthodes, another genus of Cancridae, so gradual indeed, that 

 only a slight difference in an antennary joint separates the genera ; 

 and the latter genus, includes species having the narrow form common 

 among the Eriphidae. Through the genus Chlorodius, there is the 

 same passage to closely-related species having a narrow Eriphioid or 

 Pilumnoid form ; and Cyclodius, which is identical with Chlorodius, 

 except in having a triangular form to the third joint of the outer 

 maxillipeds, has nearly an orbicular form, while Cymo, is still more 

 nearly orbicular, the breadth equalling the length. Such narrow 

 species might be supposed, from the form, to be related to Pilumnus 

 and Pilumnoides; yet the latter are distinguished by the ridge on the 

 palate. Even the narrow Cymo has not this ridge, while in Pilum- 

 noides and Actumnus it is very prominent. 



The Platyonychidae, although without the palate ridges, are narrow 

 species, with the antero-lateral margin shorter than the postero-lateral, 

 as in the Eriphidse. In the palate and outer maxillipeds, they are 

 related to Cancer and Perimela on one side, and also to the Corys- 

 toidea on the other. 



Although the CYCLINEA have but five branchiae in the exterior of 

 the branchial pyramid, this does not seem necessarily to exclude these 

 from the Cancroidea ; for the Grapsoids admit of a like variation, the 

 number being at times as great as in the Cancroids. They are related 

 to the Corystoids, as explained, in being a low grade of Cancroids, 

 rather than in having the prominent characteristic of the Corystoids. 

 The inner antennae in Corystoides, a genus near Acanthocyclus, have 

 no fossettes, and this is an example of a still lower state of degradation 

 Anomoural in character.* 



The genus Cymo has the circular outline of Acanthocyclus. But 

 the number of branchiae in the exterior of the branchial pyramid is 



* See page 54. 



