22 CRUSTACEA. 



seas. With the exception of the Orithyise, we observe but five dis- 

 tinctly marked segments in the tail of the males, while that of the 

 females presents seven. We Avill begin with those in which all the 

 feet, except the claws, are natatory. 



Matuta, Fabr. 



The Matutse have an almost orbicular shell armed on each side 

 with a very stout looth in the form of a spine; the superior edge 

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

 with pointed tuberclcsj the third joint of the external foot-jaws, 

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

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

 angled triangle. The external antennce arc very small, and the ocular 

 pedicles slightly arcuated. 



De Geer mentions a species — Cancer lalipes, 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- 

 ever(l), were brought from the East-, and the middle of that 

 margin always presents a bidenlated 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- 

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

 bular. 



But a single species is as yet knawn(2); 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(3). 



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



formed like fins(4). 



We may first separate those whose shellis almost ovoid and trans- 



(1) M. victor, Fab.; Herbst, VI, U.—3I. planipes, Fab.; Herbst., xlviii, 6; M. 

 lunaris. Leach, Zool. Miscell., cxxvii, 3—5, vai:;—!!. Peronii, lb., tab., ead., 

 1 — 2. Perhaps we should refer the fossil species called by M. Desmarest, Por^wne 

 d'Hericart, Hist. Nat. des Crust., Foss. V, 5, to this genus, or the Mursia, Leach. 



(2) Polyhius Hensloioii, Leach, Mai ac. llrit., IX, B. 



(3) The tarsi of the intermediate feet of the Portumni, Leach, are almost com- 

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



(4) Always wider and more oval than the preceding tarsi. 



