150 CRUSTACEA. 



G. 8. CYCLODIUS, Dana. Carapax parce transversus. Articulus antennae extern* 

 oblongus frontem bene attingens. Articulus maxillipedis extern! Stius triangu- 

 latus, latere interiore brevissimo. 



G-. 9. CYMO, De ffaan. Carapax non transversus, fere orbiculatus, diseiformis. 

 Antennis Chlorodio affinis. 



4. POLYDECTIN^E. Antennae internae transversae. Antennas ex- 

 ternae basi solutae, liberae. An Pilumnis propinquior ? 



G. POLYDECTUS, Edw. Orbita dentibus tribus infra instructa. Manus elongata, 

 digitis praelongis, attenuatis, uncinatis, cum dentibus tenuiter spinuliformibus 

 saepe armatis. 



SUBFAMILY I. CANCRINJE. 



Antennce internee plus minusve longitudiiwles. Frcms interoi-bitalis 

 perangustus. 



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

 narrow; and median region somewhat narrower than the breadth 

 of the carapax across the orbits. 



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

 inner antennae 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 Cancridae, 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 



