426 REPORT OF NEW JERSEY STATE MUSEUM. 



Carapace depressed, or moderately convex, very broadly trans- 

 verse or elliptical, dorsal surface uneven to smooth, with regions 

 very obscurely defined. Front lateral edges of carapace regu- 

 larly arcuated and divided into ten lobes or teeth, v^hich some- 

 times broad, subtruncated and little prominent, or sometimes 

 more prolonged and acute. Anterior lateral lobes or teeth some- 

 times armed with accessory denticles. Posterior lateral edges 

 of carapace shorter than anterior lateral edges, and defined by 

 raised line or crest (postbranchial crest). Front relatively nar- 

 row, divided into five lobes or teeth (if lobes comprising upper 

 and inner orbital angle be included) and projects somewhat be- 

 yond orbits, which small and sometimes denticulated. Teeth 

 defined by two fissures in upper and two in lower edges. Post- 

 abdomen five-jointed in male, with third to fifth joints coalescent. 

 Eyes small, set on very short thick pedicels. Antennules longi- 

 tudinally, or nearly longitudinally, plicated. Basal antennal joint 

 somewhat enlarged, with distal lobe or tooth, which unites with 

 front so as to exclude short flagellum from orbit. Exterior 

 maxillipeds with merus joints usually truncate distally, anterior 

 external angle not produced, usually more or less distinctly 

 notched on inner edge, but notch sometimes obsolete. Buccal 

 cavity completely closed by outer maxillipeds. Chelipeds usually 

 subequal and not very largely developed, their palm nearly always 

 longitudinally costated on external surface. Fingers acute and 

 dentated on inner edges. Ambulatory legs somewhat elongated, 

 dactyls slender and nearly straight. 



Species numerous, though only two on our shores. 



Key to the species. 



a. Front lateral teeth of carapace with dentate or spinuloiis edges, borealis. 

 aa. Front lateral teeth of carapace with simple dentated edges. irroratus. 



Cancer borealis Stimpson. 



Plate 133. 



Jonah Crab. 



Cancer borealis Stimpson, Ann. Lye. Nat. Hist. N. Y., VII, 1859, p. 50. 

 Cape Cod to Nova Scotia. 



