CRUSTACEA. 



150 



r 8 C YCTOi, rc s,ft>»«.-Carapax P aree transversa. Articulus antenna extern* 

 oblongus frontem bene attingens. Articulus maxilliped.s extern! 3tms tnangu- 

 latus. latere interiore "brevissimo. m _ 



G. 9 Cymo, Be iZaa«—Carapax non transversa, fere orbiculatns, disciformis. 

 Antennis CUorodio affinis. 



4 POLYDECTIN^E.— Antennse interna transversa?. Antennae ex- 

 " tern* basi solute, liberae.-An Filumnis propinquior ? 



G Polydectus, i^.-Orbita dentibus tribus infra instruct*. Manns .elongate, 

 digitis pr^longis, attenuatis, uncinatis, cum dentibus tenmter spinuliformibns 

 saepe armatis. 



Subfamily I. CANCRINiE. 



Antennce mtemce plus rninusve longitudhudes. From interoroiUilk 

 perangustus. 



Inner antennaa more or less longitudinal. Inter-orbital front very 

 narrow; and median region somewhat narrower than the breadth 

 of the carapax across the orbits. 



The Cancringe, unlike the other families of this division, have the 

 inner antennse longitudinal, and this is connected with a narrow in- 

 terval between the orbits. This inter-orbital distance in Cancer is, at 

 times, less than one-tenth of the whole breadth of the carapax, and is 

 seldom greater than one-eighth. The singularity of this ratio is evi- 

 dent, when we consider that in the other Cancridre, it varies from one- 

 sixth to one-half, and is usually one-fourth. The median region, 

 although broader anteriorly than the breadth across the orbits, is 

 seldom one-third as broad as the carapax. The narrowness of the 

 inter-orbital space accounts for the inner antennae being longitudinal. 



The carapax is convex, with the lateral portions often somewhat 

 dilated. The buccal area is usually longer than broad; and the third 

 joint is commonly a little oblong, and at times projects forward some- 

 what beyond the limits of the buccal area; the epistome is very short, 

 and sometimes obsolete. The second joint of the outer maxillipeds 



