THE GRAPSOID CRABS OF AMERICA. 17 



Subfamily Carcinoplacinae Miers. 



Carcinoplacinae Miees, Challenger Rept., ZooL, vol. 17, 1SS6, p. 222. 

 Pseudorliomhilinac Alcock, Journ. Asiat. Soc. Bengal, vol. GO, 1900, pp. 286, 

 292, and 297. 



Carapace xanthoid, the regions seldom well defined; front usually 

 of good breadth and square cut, often little deflexed ; eyes and orbits 

 usually of normal size and form, the eyes well pigmented and the 

 eyestalks normally movable except in certain deep-sea genera; the 

 antennules fold transversely; antennal fiagella of medium length. 

 Epistome well defined; buccal cavern square-cut and usually com- 

 pletely closed by the external maxillipeds, which have a subquadrate 

 merus. The base of the third segment of the male abdomen covers 

 the whole space between the last pair of legs. Male openings not 

 sternal. 



Represented in America by three genera. 



Genus TRIZOCARCINUS Rathbun. 



Trizocarcinns Rathbun, Proc. U. S. Nat. Mus., vol. 47, 1914, p. 117; type, 

 T. dentatus (Rathbun). 



Carapace deep, subquadrilateral, somewhat broader than long, with 

 little distinction of regions, convex in both directions. Fronto- 

 orbital border about three-fourths of the greatest breadth of the 

 carapace; antero-lateral borders arched, dentate. 



Front square-cut, straight, faintly notched in the middle, distinctly 

 separated from the supra-orbital angles, between one-third and oue- 

 fourtb the width of the carapace. Upper margin of orbit with 2 

 distmct notches. Basal antennal joint short, the flagellum standing 

 loosely in the orbital hiatus. The antennules fold transversely. 



Buccal cavity widening distally, not completely closed by the 

 maxillipeds, the merus of which has a concave anterior margin, and 

 the antero-external lobe projects forward not outward. Efferent 

 branchial channels well defined. A stridulating ridge formed of 

 parallel striae runs obliquely backward from the antero-external 

 angle of the buccal cavity ; and is played upon by a short ridge on the 

 merus of the chelipeds. 



Chelipeds equal, much more massive than the legs. In both sexes 

 all seven abdominal segments are distinct, and in the male the third 

 segment covers the whole width of the sternum between the bases 

 of the last pair of legs. 



This genus is closely related to the Indo-Pacific genus Carcinoplax^ 

 but differs in the form of the merus of the maxillipeds, in the notch 

 separating front and orbital angle, the superior notches of the orbit, 

 and the stridulating ridges. 



Only one species known. 

 65863—17 2 



