12 TRUE CRABS OF MONTEREY BAY 



Key to the Families of the Tribe Brachyura. 



o. Second antennae long (flagellum equal to more than half the width of 

 the carapace) ; first antennae without special fossettes, first ab- 

 dominal legs of female present, uropods rudimentary or absent, 

 female openings in coxae of legs, gills numerous. 



Subtribe DROMIACEA, Fam. Dromiidae 



aa. Second antennae short (never equal to half the width of the carapace) 



first antennae usually lodged in special fossettes, first abdominal 



legs of female wanting, uropods never present, female openings 



in sternum (rarely in coxae), gills few. 



b. Buccal frame triangular, narrowed forward; efferent branchial 



channels opening at middle of endostome. 



Subtribe OXYSTOMATA 



c. Last I or 2 pairs of legs reduced in size and articulated higher 



than preceding pairs, so as to lie on dorsal surface of 



body. Fam. Dorippidae 



cc. Legs normal in size and position. 



d. Maxillipeds closing the buccal cavern; the palp hidden 



by the triangular merus. Fam. Leucosiidae 



dd. Maxillipeds not completely closing the buccal cavern; 



the palp always exposed. Fam. Calappidae 



bb. Buccal frame quadrate; efferent branchial channels opening at 



sides of endostome. Subtribe BRACHYGNATHA 



c. Carapace usually triangular, with pointed or spined rostrum ; 



the branchial region inflated, the hepatic region small ; 



orbits usually incomplete. Superfam. Oxyrhyncha 



d. Basal antennal joint very small and short, not reaching 



farther forward than posterior margin of orbit; 



hard basal joint of antennule reaching orbit and 



forming part of inferior margin. Chelipeds much 



longer and more massive than other legs. 



Fam. Parthenopidae 

 dd. Basal antennal joint well developed, reaching at least to 

 anterior margin of orbit, of the lower margin of 

 which it forms the greater part ; basal antennular 

 joint usually soft and concealed in fossette, never 

 reaching orbit. Chelipeds not markedly longer 

 or more massive than other legs. Fam. Inachidae 



