B R A C H Y U R A. 71 



in the number of branchiae being but nine, as in the Maiinea. The posi- 

 tion of the genus between Dromia, and the long-legged Maiinea is 

 evident, but its closest relations are with the former, as shown by De 

 Haan. The genus Oncinopus is, in our view, a genus on the same 

 line of transition, between Latreillia and the Maiinea, but belongs 

 with the latter. 



Such objections we are disposed to offer to the higher divisions in 

 the system of De Haan. It is in the lower subdivisions that the 

 maxillipeds are relied upon, to the exclusion, mostly, of more impor- 

 tant characteristics. 



In the subdivisions of the Cancroidea, the groups Cancer, Corystes, 

 Grapsus, Ocypoda, and Portunus (called by De Haan genera), are 

 characterized by reference to the first and third maxillipeds. The 

 insertion of the fourth joint of the outer maxillipeds remote from the 

 inner apex of the third, separates Ocypoda and Grapsus from the rest. 



In his synoptical table of genera of the Cancroidea, Corystes and 

 Cancer differ in the former having the third joint of the outer maxil- 

 lipeds obkmg-qttadrote or elongate, and the latter quadrate or transverse. 

 Yet in half the genera of the Corystes group, the form of this joint is 

 not oblong, and in some genera of the Cancer group it may be elon- 

 gate. In the genus Cancer, this joint is usually oblong, and it often 

 overlaps somewhat the epistome, as in many Corystidea. Even in the 

 genus Xantho, in which this joint is usually transverse or quadrate, 

 it is sometimes much elongate, as is seen in X. Orbit/mi (Edw. and L.), 

 in which it resembles what is seen in some Corystes, though not ex- 

 panded over the epistome. When we consider that these outer maxil- 

 lipeds are only modified legs, we feel at once the fact that such varia- 

 tions are of small moment, nothing in fact, but the more or less 

 extension of a margin; only the connexion of such a variation with 

 the necessities of some vital function in the animal, could give it a 

 wide value in classification. 



The group Portunus is naturally distinguished by their having 

 a peculiar lobe to the inner margin of the interior branch of the 

 first maxillipeds. The detection of this important character is due to 

 De Haan. Platyonychus and Carcinus are thus excluded from the 

 group, and on account of the character of the outer maxillipeds, De 

 Haan places these genera in his group Corystes, to the species of 

 which they bear some resemblance in form. In our view, these and the 

 allied genera more properly constitute a distinct family, near the Por- 

 tunus group. The large outer antennae of the Corystes group, flexed 



