I go 



Oediplax Rathbun, Proc. U.S. Nat. Mus., v. i6, 1893, p. 241. Species: O. granulata from the 



Gulf of California. 

 Tetraplax Rathbun, Bull. U.S. Fish Comm. for 1900, v. 2, 1901, p. 9. Species: Trevillea" 



quadridetitata Rathbun, Bull. Lab. Nat. Hist. State Un. Iowa, v. 4, 1898, p. 287, 



pi. 8, f. I. Hab. West India. 

 Cyrtoplax Rathbun, Proc. U.S. Nat. Mus., v. 47, 1914, p. 118, pi, 2. Species: " Eucratoplax' 



spinidentata Benedict, John Hopkins Un. Circ, v. 11, n" 97, 1892, p. 77; Rathbun, 



Ann. Inst. Jamaica, v. i, 1897, p. 26; "Eucratopsis' spin. Rathbun, Bull. Lab. Nat. 



Hist. State Un. Iowa, v. 4, 1898, p. 281 ; Bull. U.S. Fish Comm. for 1900, v. 2, 



1901, p. II. Hab. West India. 

 Chasmophora Rathbun, Proc. U.S. Nat. Mus., v. 47, 1914, p. 119. Species: " Eucratopsis' 



jnacrophtkalma Rathbun, Proc. U.S. Nat. Mus., v. 21, 1898, p. 601, pi. 43, f 3 — 4, 



from Panama. 

 Homoioplax Rathbun, Proc. U.S. Nat. Mus., v. 48, 19 15, p. 146. Species: "Pseudorkomiila" 



vestita var. sexdentata (Haswell) Miers, Zool. H. M. S. "Alert", 1S84, p. 240, pi. 24, 



f B. Hab. Indo-Malayan Arch. 



A primary division between the genera, though based on the cf only, has been proposed 

 by Miers ^) : one, in which the last segment of the sternum is for the greater part concealed, 

 the anterior corners being only visible, and another, in which this last segment is largely 

 exposed. To the first group the following genera would belong : Eiiryp/ax, Eucratopsis^ 

 Panoplax, Oediplax and Homoioplax, to the second : Speocarcinus, Eucratoplax^ Prionoplax, 

 Cyrtoplax and Chasmophora. Glyptoplax is left aside on account of its doubtful affinities to 

 the Prionoplacinae, and I am uncertain as to the exact place of Tetraplax, as the original 

 description of " Frevilled' quadridentata is inaccessible to me; in Miss Rathbun's paper of 1901 

 the abdomen is said to be narrower than the sternum and most likely it would therefore belong 

 to the second group. 



As results from the list given here nearly all the genera are American, the species 

 living either at the Atlantic or the Pacific coasts, in shallow water. Homoioplax forms the only 

 exception. The "Siboga" not only dredged the only species of the latter genus, but also two 

 other species of the Prionoplacinae, one belonging to Speocarcinus, and another constituting 

 apparently a new genus. 



I. Homoioplax haswelli (Miers) Rathbun. PI. 10, Fig. i. 



1884. Pseudorhombila vestita (de Haan) var. sexdentata (Haswell) Miers. Zool. H. M. S. "Alert", 



p. 240, pi. 24, f. B. 

 1886. Pilnnmoplax vestita vax. sexdentata (Haswell) Miers. Rep. "Challenger", Brachyura, p. 229. 

 191 5. Homoioplax haswelli Rathbun. Proc. U.S. Nat. Mus., v. 48, p. 146. 



Stat. 2. Madura Strait, south of Madura. Depth 56 m. i cf. 

 Miers supposed that this species was nearly related to ''Cnrtonotus" vestitns de Haan, 



I) Rep. "Challenger", Brachyura, 1886, p. 222. 



42 



