286 MANUAL OF NATURAL HISTORY. 



moveable peduncles ; rings of thorax covered by a 

 carapace. 



I. OEDER DECAPODS (Decapoda). 



Five pairs of ambulatory legs ; gills at their base, 

 under the thorax; mouth with five pairs of feet- 

 like jaws ; head covered by the thorax. 



1. SUB-ORDER. SHORT-TAILED DECAPODS (Brachyura). 



Abdomen slightly developed, not serving for nata- 

 tion, folded under body, without appendages. 



1. FAMILY. Spider-Crabs (Inachidse). Carapace 



triangular, beaked in front; fore-legs short, 

 slender, second and third pairs very long ; 

 third joint of outer foot-jaws not bearing the 

 next joint at its anterior and inner angle. 



2. FAMILY. Spiny-Crabs (Maiidse), Carapace spiny, 



sub-triangular, with two horns in front ; fore- 

 legs longer and thicker than second pair ; 

 third joint of outer foot-jaws with the fourth 

 joint on its anterior and inner angle. 



3. FAMILY. Long -armed Crabs (Parthenopidse). 



Carapace triangular, tubercular, entire or 

 simply grooved in front ; fore-legs greatly 

 developed, hand triangular, pincers recurved, 

 other legs short. 



4. FAMILY. True-Crabs (Canceridse). Carapace 



convex, rounded at margins ; fore-legs usually 

 very large and prehensile, ending in strong 

 pincers, the others short and ambulatory ; 

 third joint of outer foot-jaws quadrilateral, 

 not truncate at its front inner angle. 



