DECAPOD A. 163 



female present! seven, \\Vwill begin with those in which all the 



feet, except the elaws, are natatory. 



MATUTA, Fabr. 



The Matuta 1 have an almost orbicular shell armed on each side 

 with a v TV stout tooth in the form of a spine; the superior edge 

 of the hands dentated like a crest, and their external face studded 

 with pointed tuhercles; the third joint of the external foot-jaws, 

 without any apparent emargination, terminates in a point, so that 

 it form*, with the preceding joint, an elongated and almost right- 

 angled triangle. Tho external antennae are very small, and the 

 ocular pedicles slightly arcuated. 



De Geer mentions a species Cancer latipes, which he says is 

 from the American seas, and has its front terminated by a 

 straight and entire margin. All those we have seen, how- 

 rver*, were brought from the East, and the middle of that 

 margin always presents a bidentated or emarginated projection. 



The 



POLYBIUS, Leach, 



Is allied to the Portuni, but the shell is proportionably narrower 

 and more rounded ; the sides are merely furnished with ordinary 

 teeth. The third -joint of the external foot-jaws is obtuse and emar- 

 gii luted. The eyes are much thicker than their pedicles, and glo- 

 bular. 



But a single species is as yet known f; it was found on the 

 coast of Devonshire, and has also been observed by M. D'Or- 

 bigny on the sea-coast of the western departments of France J> 



In all the following swimmers, the two posterior feet only are 

 formed like fins . 



We may first separate those whose shell is almost ovoid and trans- 

 versely truncated before, and where the tail of the males (the only 

 > x known) consists of seven distinct segments. Such is the 



ORYTHYIA, Fabr. 



The only species known, Orith. mammillari*, Fabr., Cancer 

 bimnciilnfiK, Herbst., XVIII, 101, is found in the sea of China, 

 or at least forms a part of the collections of Insects sold by its 

 inhabitants to foreigners. The ocular pedicles are longer in 

 than those of the Portuni. 



* M. rir/or, Fab. ; Herbst., VI, 44. M. planipes, Fab. ; Herbst., xlviii, 6 ; M. 

 lunar, SooL Mi-rell., cxxvii, 35, Mir. ;M. Peronii, Ib., tab., cad., 



1 2. Perhaps \re should refer the fossil species called by M. Desmarest, Fortune 

 tfHtricart, Hist. Nat. des Crust., Foss. V, 5, to this genus, or the MURSIA, 

 Leach. 



f Polybiu* Henslowtt, Leach, Malar. Hrit., IX, B. 



J The tarsi of the intermediate feet of the Portumni, Leach, are almost com- 

 pressed into a fin; they might be placed after the Polybii. 



Always wider and more oval than the preceding tarsi. 



M 2 



