OXYSTOMATOUS AND ALLIED CRABS OF AMERICA 265 



Family GONEPLACIDAE Dana 



Cronoplacidae Dana, Amer. Journ. Sci., ser. 2, vol. 12, p. 285, 1851; United States 

 Exploring Expedition, Crustacea, pt. 1, pp. 208 and 310, 1852; pt. 2, p. 1425, 

 1853.— Alcock, Journ. Asiat. Soc. Bengal, vol. 69, pp. 283, 286, 292, 297, 

 and synonymy, 1900. 



Goneplacidae Rathbun, U. S. Nat. Mus. Bull. 97, p. 15, 1918. 



The palp of the external maxillipeds articulates at or near the 

 anterointernal angle of the merus; the exognath is of normal size 

 and is not concealed. The interantennular septum is a thin plate. 

 The division of the orbit into two fossae is usually not indicated. 

 The genital ducts of the male usually perforate the base of the last 

 pair of legs, often passing forward through a groove in the sternum. 



Subfamily Carcinoplacinae Miers 



Carcinoplacinae Miers, Voyage of H. M. S. Challenger, Brachyura, vol. 17, p. 



222, 1886.— Rathbun, U. S. Nat. Mus. Bull. 97, pp. 16, 17, 1918. 

 Pseudorhombilinae Alcock, Journ. Asiat. Soc. Bengal, vol. 69, pp. 286, 292, and 



297, 1900. 



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 four genera, the other three of which 



have been previously discussed in Bulletin 97, "The Grapsoid Crabs 



of America." 



Genus GERYON Kr0yer 



Geryon Kr0yer, Nat. Tidsskrift, vol. 1, p. 1, pp. 20-21, 1835 (type, G. trident 



Kroyer). 

 Chalaepus Gerstaecker, Arch, fiir Naturg., vol. 22, pt. 1, p. 118, 1850 [type, 



C. trispinosus (Herbst)]. 



Carapace broader than long, anteriorly arcuate, posteriorly trun- 

 cate, longitudinally strongly convex; front broad, deflexed, but little 

 arcuate; anterolateral margins not recurved and provided with 

 strong teeth. Branchial region prominent, hepatic region less so; 

 eye peduncles short, stout; lower margin of orbit separated from the 

 front, and orbit separated from the antennular fossa; superior margin 



