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 Mam and 

 Cancer -roups have even closer relations than the Cancer and Grapsus 

 -roups ° The former are related in most of the prominent characters, 

 —the branchial, buccal, abdominal, and genital; although so unlike m 

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

 antennse 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 branchiae, 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, ami in 

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

 unlike the Maiinea; in the longitudinal inner antenmv 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 antenna*. 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 Braehvura 

 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 vulva- in tin' base of 

 the third pair of legs. De liaan 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 vulva- moreover, they were known to have 

 no fbssettes for the inner antennas, and the outer antenmv tree and 

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

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



