354 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.21 



2b. Rostral horns subtruncate or tuberculiform 



4a. Carapace not paved with close-set granules, occasionally 

 some of the areolations granulate. Male first pleopod 

 without tubular extension, tip pointed 



5a. Only three or four anterolateral spines or tubercles, 

 some occasionally with accessory spines or tubercles 



6a. Three spines on basal segment of antenna. 

 Four anterolateral protuberances, the last sim- 

 ple and acute, the others subdivided into two 

 or three spines each.* Male first pleopod with 

 a single subterminal fold . . sinensis 



6b. Two blunt teeth on basal segment of antenna. 

 Areolations of carapace granulate; two lobes 

 and one (or two) spine (s) on anterolateral 

 margin. Male first pleopod with two subtermi- 

 nal flanges .... tuberculatus 



5b. Six or more anterolateral spines or spinules. Ros- 

 tral lobes truncate. Chelipeds and ambulatory legs 

 elongate. Antennae long and slender. Male first 

 pleopod with a subterminal swelling. Size small 

 pygjnaeus 



4b. Carapace paved with close-set granules. Lateral mar- 

 gins of carapace with lumpy projections. Wrist tuber- 

 culate above. Male first pleopod with a tubular exten- 

 sion. Size large. Galapagos only . . . belli 



lb. Carapace smooth and bearing oblique branchial sulci, either 

 strongly or weakly indicated. Intermediate orbital teeth tuber- 

 culiform, inconspicuous . . . (Subgenus Mithraculus) 



7a. Three anterolateral marginal lobes. Inner edge of cheliped 

 laminate to middle of manus. Carapace narrower than 7b. 

 Male first pleopod with a sheath extending beyond terminal 

 opening. Galapagos only nodosus 



7b. Two lobes and a spine on anterolateral margin. Inner edge 

 of wrist only laminate, lamina faintly bilobed. Carapace 

 wider than long by nearly half. Male first pleopod with 

 two rounded flanges denticulatus 



*In Mithrax (Mithrax) sinensis clarionensis into five spines each. 



