70 CRUSTACEA. 



of structure, not less fundamental, or of less functional value, than that 

 distinguishing the Leucosia section. 



In the first of the grand divisions of De Haan, the Cancer and 

 Grapsus groups are embraced under the tribe Cancroidea, while the 

 Maia group is a distinct tribe. Yet it is evident that the Maia and 

 Cancer groups have even closer relations than the Cancer and Grapsus 

 groups. The former are related in most of the prominent characters, 

 the branchial, buccal, abdominal, and genital ; although so unlike in 

 the narrow front, the more posterior position of the parts within, the 

 antennae and other points, as to authorize a separation of the two. 

 While the Grapsoid species are remote from the Cancroids, not only in 

 general form, but more essentially in the number of branchiae, the in- 

 sertion of the male sexual appendages, and the articulations of the outer 

 maxillipeds, which here take a peculiar character, sustained through 

 nearly all the group. 



Trichidea includes the single genus Trichia in form near a slightly 

 transverse Mithrax or a Parthenope; in number of branchia), male 

 appendages, and abdomen, like the Maioidea and Cancroidea; in the 

 first basal joint of the outer antenna* being situated in a hiatus of the 

 orbit, not projecting beyond it, bounded by a suture outside, and in 

 the character of the orbit, like Parthenope and most Cancroidea, and 

 unlike the Maiinea; in the longitudinal inner antennae like Parthe- 

 nope and other Maioidea. In all its essential characters, it is related 

 to Parthenope. The form of the maxillipeds is near the same in 

 Dromia, which genus has also similar antennae. But Dromia is also 

 related to Parthenope ; yet, unlike Trichia, it is a degraded form, verg- 

 ing towards the Macroura, as has been explained. 



The Dromiacea are evidently intermediate between the Brachyura 

 and Macroura in the characters alluded to ; and although nearer the 

 former than the latter, they are best retained in the tribe Ano- 

 moura. No species but these transition forms have the number of 

 branchiae larger than the normal number, or the vulvse in the base of 

 the third pair of legs. De Haan has transferred to Dromiacea, the 

 genus Latreillia. He has greatly increased our knowledge of these 

 species, showing that they have the posterior legs of a Dromia, and 

 the same position to the vulvae; moreover, they were known to have 

 no fossettes for the inner antenna), and the outer antennae free and 

 moveable to the base. These are all characters of the Anomoura; 

 and there is but one essential point in which they are different, 



