THE BE ACHY U RA AND MACRUEA OF PORTO RICO. 
5 
Suborder BRACHYURA. The Crabs. 
Key to the Porto Rican tribes and families of the suborder Brachyura. 
A. Buccal frame quadrate; efferent branchial channels opening at sides of endostome. 
B. Carapace usually quadrilateral. Frontal region curved downward. Verges of the male inserted either in 
sternal plastron or in the basal joints of fifth pair of legs, thence passing through channels in 
sternum beneath the abdomen Tribe Catometopa 
C. Carapace hard and firm. Front, orbits, and eye-stalks not very small. Buccal frame quadrate anteriorly. 
1). Last pair of legs not remarkably short nor subdorsal. 
E. Carapace moderately convex or depressed; branchial regions not greatly dilated. 
F. Third maxillipeds with palpus articulated usually at front inner angle of merus. Front of moderate 
width or very narrow. Eye-stalks often greatly elongate Family OcYPontD.® 
F'. Third maxillipeds with palpus articulated at apex or front outer angle of fourth. Front usually 
broad. Eye-stalks of moderate size Family Grapsida: 
E'. Carapace very convex, especially dilated over and in front of branchial regions; antcro-lateral 
margins entire and strongly arcuate. Last joint of walking legs often armed with longitudinal 
rows of spines Family Gecap.ciniile 
D'. Last pair of legs very short and subdorsal Family Palicidas 
C'. Carapace more or less membranaceous. Front, orbits, and eye-stalks very small. Buccal frame arcuate 
anteriorly. Species of small size Family Pinnotheridas 
B'. Carapace not-quadrilateral. Verges of male inserted in basal joints of fifth pair of legs. 
C. Carapace broad, short, rounded anteriorly, without projecting frontal rostrum Tribe Qyclomelopa 
D. Terminal joints of last pair of legs not flatly expanded. 
E. Terminal joints of last pair of legs usually spinuliferous. Species fluviatile, or living in damp eartli 
away from the sea Family Potamonid* 
E'. Terminal joints of last pair of legs usually unarmed. Species marine Family Pilumnid/E 
D'. Terminal joints of last pair of legs usually flatly expanded. Front well separated from inner orbital 
angles Family Portuniu/E 
C'. Carapace usually triangular, with projecting pointed or spined rostrum Tribe Oxyrhyncha 
D. Basal joint of antennae well developed, inserted beneath the eyes, and usually forming a great part of 
infraocular space Family Maud.® 
])'. Basal joint of antennse very small, and with the next joint embedded in the narrow gap between front 
and inner orbital angle Family Parthenopid.® 
A'. Buccal frame usually triangular, narrowed forward; efferent channels opening at middle of endostome. 
Verges of male inserted in basal joints of fifth pair of legs Tribe Oxystomata 
B. Last one or two pairs of feet not articulated higher up than the preceding pairs. 
C. Afferent channels to branchiae opening behind pterygostomian regions and in front of chelipeds. 
I). Palpus of the outer maxillipeds not concealed . .Family Gala pim das 
D'. Palpus of the outer maxillipeds concealed behind triangular acute merus Family Matutid.e 
C'. Afferent channels to branchiae opening at antero-lateral angles of endostome Family Leucosiid/E 
B'. Last one or two yjairs of feet articulated higher up than preceding pairs Family Dorippidas 
Tribe CATOMETOPA or GRAPSOIDEA. 
Carapace broad anteriorly, often subquadrate, sometimes subglobose, truncate or arcuate anteriorly, 
but not rostrate. Front bent downward. Epistome short, often almost linear. The pairs of branchiae 
are usually fewer than nine in number; the efferent channels open at the sides of the endostome. The 
male verges are inserted either in the sternal plastron or in the basal joints of the last pair of legs, 
thence passing through channels in the sternum beneath the pleon. 
Family 0 CYP 0 D 1 DJE Leach, 1819. 
Carapace in general moderately convex, either cancroid or trapezoidal, with antero-lateral margins 
straight or arcuate, the branchial regions not generally dilated. The front is of moderate width or 
very narrow. The orbits and eye-stalks are of moderate size or greatly developed. The chelipeds in 
the adult male are in general of moderate size, sometimes slender and elongate. The seventh joint in 
the walking legs is styliform, without strong spines. The pleon does not always cover the whole width 
of the sternum between the last pair of legs. 
