APPENDIX TO CHAPTER VII 123 



Body mostly depressed ; antennae short ; 

 abdomen short and folded under the cepha- 

 lothorax, with 1 to 4 pairs of appendages, 

 and usually without tail-fin [superfamily 

 Brachyura]. 



Ci. Male duct opens on thoracic plate ; ce- 

 phalothorax usually quadrangular, at 

 times transversely oval; anterior lateral 

 area (liver area) of carapace small ; 

 usually fewer than 9 pairs of gills; orbits 

 look forward or obliquely downward . Catometopa 



(Square Crabs; Fiddler-crabs) 

 C 2 . Female opening on broad thoracic plate ; 

 male opening on coxa of 5th pair of 

 thoracic legs ; 9 pairs of gills. 

 d]_. Cephalothorax broad, diminished be- 

 hind, bowed in front ; liver area 

 large ; orbits directed obliquely up- 

 ward and forward .... Cyclometopa 



(Arched Crabs) 

 dz- Cephalothorax triangular, anteriorly 



pointed, with longer or shorter ros- 



V 



trum ; liver area small ; orbits di- 

 rected outward .... Oxyrhyncha 



(Triangular Crabs ; Spider-crabs) 

 Body mostly elongated ; antennae long ; ab- 

 domen long, not bent under, or only partly 

 so, typically with 5 pairs of legs and a large 

 tail-fin [superfamily Macrura]. 

 c\. Last pair of thoracic legs shoved back- 

 ward and rudimentary. 

 d\. Last thoracic segment not free ; ab- 

 domen with hard shell, hinder half 

 turned under ; first pair of legs 

 typically non-chelate . . . Hippidce 



(Mole-crabs) 

 c? 2 - Last thoracic segment free ; abdomen 



typically with thin cuticula, un- 

 symmetrical and with rudimentary 

 legs ; first pair of legs very large, 

 chelse unsyrnrnetrical , . Paguridce 



(Hermit-crabs) 



