272 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



KEY TO THE SUBORDERS, TRIBES, AND FAMILIES OF THE ORDER DECAPODA, 

 REPRESENTED ON THE WEST COAST OF AFRICA. 



A. Body short, with the carapace visually wide and triangular, rounded or quadrate, 

 and the sternal surface excavated and covered by the abdomen, 

 which is folded forward and narrow in the males, but wide in 



the females Suborder BRACHYURA. 



B. Branchiie not more than nine. 



C. Buccal frame quadrate; efferent branchial channels opening at sides of 



eudostome. 



D. Carapace quadrilateral. Frontal region curved downward. Verges of 



male inserted either in sternal plastron or in basal joints of 



iifth pair of legs, thence passing through channels in sternum 



beneath abdomen Tribe C atometopa. 



E. Carapace hard and firm. Front, orbits, and eyestalks not very small. 

 Buccal frame quadrate anteriorly. 

 F. Carapace moderately convex or depressed; branchial regions not 

 greatly dilated. 

 G. Third maxillipeds with fifth joint articulated at the front inner 

 angle usually. Front of moderate width or very narrow. Eye- 

 stalks often greatly elongate Family ocypodid^. 



G'. Third maxillipeds with fifth joint articulated at apex or front outer 

 angle of fourth. Front usually broad. Eye-stalks of moderate 



size Family grapsid^. 



F'. Carapace very convex, especially dilated over and in front of the 

 branchial regions; antero-lateral margins entire and strongly 

 arcuate. Seventh joint of walking legs often armed with longi- 

 tudinal rows of spines. Laud crabs Family gecarcinid^. 



E'. Carapace more or less membranaceous. Front, orbits, and eyestalks 

 very small. Buccal frame arcuate anteriorly. Species of small 

 size, and may be found in shells of bivalve mollusks, tests of sea- 

 urchins, and tubes of annelids Family PiNNOTHERiDiE. 



D'. Carapace not quadrilateral. Male genital openings on the basal joint of 

 the fifth pair of legs. 

 E. Carapace broad, short, rounded anteriorly, without projecting frontal 



rostrum Tribe C yclometopa. 



F. Buccal cavity well defined. Antennulte folded transversely or ob- 

 liquely transversely. 

 G. Carapace convex. Terminal joint of last pair of legs not fiatly 

 expanded. 

 H. Termiualjointof the last pair of legs usually spinuliferous. Species 

 fluviatile or living in damp earth away from the sea. 



Family potamonid^. 

 H'. Terminal joint of last pair of legs usually unarmed. Species 



marine Family pilumnid^. 



G'. Carapace depressed, widest at the last antero-lateral marginal 

 spine. Usually from 5 to 9 antero-lateral teeth or spines. Ter- 

 minal joint of last pair of legs usually flatly expanded. 



Family portunid^. 

 F'. Buccal cavity not sharply defined, the third maxillipeds usually 

 extending over its anterior margin. Antennulse folded longi- 

 tudinally Family cancrid^. 



E'. Carapace usually triangular, with projecting pointed rostrum. 



Tribe Oxyrhyncha. 

 F. Basal joint of antenniie. well dcA^eloped, inserted beneath the eyes and 

 usually forming a great part of the infra-ocular space. 



Family maiid.«. 



