THE SPIDER CRABS OF AMERICA 9 



SYSTEMATIC DISCUSSION 



Order DECAPODA 

 Suborder Reptantia 



Tribe BRACHYURA 



SUBTRIBE BRACHYGNATHA 



Superfamily OXYRHYNCHA 



KET TO THE SUBTRIBES OF THE TRIBE BRACHYURA 1" 



A'. Mouth field (endostome) prolonged forward to form a gutter. Last pair of 

 legs normal or abnormal. Female openings generally sternal. First 



abdominal limbs of female wanting. Gills few Subtribe Oxystomata. 



A*. Mouth field roughly square. 



Bi. Last pair of legs abnormal, dorsal. Female openings coxal. First abdom- 

 inal limbs of female present. Gills usually many Subtribe Dromiacea. 



B^^. Last pair of legs normal, rarely reduced, not dorsal, except in Cymopolia 

 and Retropluma. Female openings sternal. First abdominal limbs of 

 female wanting. Gills few Subtribe BRACHYGNATHA, p. 9. 



KEY TO THE SUPERFAMILIES OF THE SUBTRIBE BRACHYGNATHA. 



A'. Fore part of body narrow, usually forming a distinct rostrum. Body more or 

 less triangular. Orbits generally incomplete. 



Superfamily OXYRHYNCHA, p. 10. 

 A*. Fore part of body broad. Rostrum usually reduced or wanting. Body 

 oval, round, or square. Orbits nearly always well enclosed. 



Superfamily Brachyrhyncha. 



KEY TO THE FAMILIES OF THE SUPERFAMILY OXYRHYNCHA 



A'. Carapace not thin and fiat. Chelipeds either mobile or powerful, with bent 



fingers. Male opening coxal. 



B'. Chelipeds especially mobile, rarely much greater than the other legs, or 



with fingers bent at an angle with the hand. Second article of antenna 



well developed, generally fused with epistome and often with front. 



Orbits generally more or less incomplete. Hooked hairs almost always 



present Family MAJIDAE, p. 10, 



B*. Chelipeds not specially mobile, usually much longer and heavier than the 

 other legs, and with fingers bent on the hand at an angle toward the side 

 on which the fixed finger is set. Second article of antennae small, 

 short, and not fused with epistome or front. Orbits well made. Hooked 



hairs almost always wanting Family PARTHENOPIDAE, p. 510. 



A^. Carapace thin and flat. Chelipeds not long or specially mobile or with 

 fingers bent at an angle with the hand. Male opening sternal. [No 

 orbits. Second article of antennal stalk slender, fused with epistome but 

 not with front. No hooked hairs] Family HYMENOSOMIDAE, p. 561. 



'» The keys to the subfamilies and higher groups are taken mostly from Borradaile's work above cited. 

 Those names in the right-hand margin which are printed in capitals indicate the subfamilies and higher 

 divisions treated of in this volume. 



