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Zoology. 123 



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RuppeUia of Edwards, and Eudora of De Haan, have the same 

 typical species. But De Haan neglected to observe in the type the 

 important peculiarity of the orbit, (its being wholly closed within so as 

 to exclude the base of the outer antennae, a peculiarity found in no 

 Brachyura except a (ew of the Eriphidae,) and hence his genus includes, 

 according to his own use of it, some Xanthoid species. The two names 

 are by no means synonyms; and adopting the group as laid down by 

 Edwards, we are forced to adopt his generic name. Modificaiions to 

 some extent may be made in accepted genera, and this we have at- 

 tempted in some instances below, but not the complete perversion that 

 would happen by giving De Haan's name to Edwards's genus. 



De Haan has not recognized the distinction between the pointed and 

 spoon-shape figures as a generic characteristic, and this makes some 

 difficulty in substituting his names for those of Edwards, where the 

 groups are otherwise similar. This characteristic was first employed 

 by Leach and subsequently by Edwards. The genera of the two kinds 

 often graduate into one another : but the parallel relation between the 

 series is best shown by retaining them apart in separate subfamilies. 

 Between our Xanthine and Chlorodinre there is nearly a perfect paral- 

 lelism. De Haan's species of the genus Xantho are in part Chlorodii. 



De Haan has multiplied much the genera of swimming Crabs, by 

 subdividing Lupa and Thalamita. This has partly arisen from an un- 

 warranted reliance for the characteristic on the form of the 3d joint of 

 the outer maxillipeds, as well as on that of the inner branch of the 1st 

 niaxillipeds. 



In a former paper it AVas observed that the 3d joint of the outer max- 

 illipeds may undergo great variations in proportion in the same genus. 

 This is well illustrated among the Portunidcc. Amphilrite of De Haan 

 (a subdivision of Lupa) is described as having this joint slwri and ob^ 

 lique. But in species of true Amphilrite, it varies from this form to a 

 form unusually oblong. Again he makes Neptunus and Achelous 

 differ from Amphilrite in having this joint more oblong, the reverse of 

 which is actually the fact among many of the species examined by the 

 writer. So Thalamita is characterized by having this same joint 

 short, wht^n In fact it is sometimes longer than broad. The form 

 in one species (T. Integra, 2?.) scarcely "differs in relative length or 

 obliquity from that of Lupa dicantha. Again Oceanvs (Thalamita 

 crucifera of Edwards) is said to have the inner branch of the 1st max- 

 ilhpeds three-Iobed, and Thalamita, as having the inner margin uni- 

 dentate. The latter has the inner lobe as in Oceanus, and this makes 

 fhe one tooth ; (he margin outside of this lobe or tooth, is straight at top 

 in some species (T. crassimana and crenata), but excavate in others, 

 becoming even deep and angulate in TL integruy a species very near 

 ^dmetus in form and general characters. There is thus a gradual 

 iransuion to the form in Oceanus. Such variations in this margin are 

 luerefore unimportant, as many other cases illustrate. 



"iJr grand divisions are named after the larger to which they ap- 

 proximate. This plan might be carried farther with much profit. 

 Anus among the five families of Cancrinea— the Cancridre, are the 

 ^ancrinca Typica ; the Eriphidse, are the Cancrinea Grapsidica, for in 

 ^ ndges of the palate as well as form they approximate to Grapsus ; 



