20I 



Merus of external maxillipeds suboval, antero-external angle 



not produced. Abdominal segments of cT partly coalesced . Chasmocarcinus Rathbun ^) 

 Lateral margins of carapace strongly convergent backward . 7 



7. Margins of carapace everywhere marked by a prominent ridge, 



fronto-orbital border measuring two-thirds of greatest width 

 of carapace. Merus of external maxillipeds very broad and 

 as long as ischium. Dactyli of two last pair of legs short, 



about half as long as propodites Paranotonyx Nobili -) 



Margins of carapace not marked by a prominent ridge, fronto- 

 orbital border measuring one-half of greatest breadth of 

 carapace 8 



8. Front bilobed, with longitudinal sulcus. Walking legs almost 



naked, meropodites of penultimate pair of legs with a tooth 

 at posterior margin, dactyli extremely short, scarcely one- 

 third of the length of the much thickened propodites . . Selwynia Borradaile ^) 

 Front not bilobed, without longitudinal sulcus. Walking legs 

 thickly fringed with hairs, meropodites of all the legs un- 

 armed, dactyli about as long as propodites Par^selwynia n. g. 



9. Carapace much broader than long 10 



Carapace only a litde broader than long; postero-lateral 



margins divergent backward 12 



10. Postero-lateral margins of carapace mostly parallel. Merus of 



external maxillipeds not produced at antero-external angle 1 1 

 Postero-lateral margins of carapace somewhat convergent 

 backward. Merus of external maxillipeds slightly produced 

 at antero-external angle. Wrist of cheliped with the inner 

 angle spiniform. Ambulatory legs slender, penultimate pair 

 more than 2^3 times the length of carapace Rhizopa Stimpson *) 



11. First abdominal segment of cf broadened, but by far not 



filling up the interspace between the coxopodites of the 



last pair of legs Typhlocarcinus Stimpson 



1) This genus was founded on the species Ch. lypUiis Rathbun (Bull. Lab. State Un. Iowa, v. 4, 1898, p. 2S5, pi. 7, f. 3—5), 

 dredged N. of Trinidad, and an additional species, Ch. obliqiius, (1. c, p. 286, pi. 7, f. 6) was described at the same time, from the 

 Bahamas. In the same year the author added a third species, C. lalipes (Proc. U. S. Nat. Mus., v. 21, p. 602, pi. 43, f. 5) from Magdalena 

 Bay, Lower California, and in 1901 a fourth species, Ch. cylindricus (Bull. U.S. Fish Comm. for 1900, v. 2, 1901, p. 10, textfig. i) 

 from Porto Rico. 



Until recent years the genus was thus known only from American waters, but now a fifth species has lately been described by 

 Miss Rathbun {Ch. cavimanus, Proc. U. S. Nat. Mus., v. 48, 1914, p. 149) from Philippine waters, from the rather considerable depth 

 of 300 fathoms. The "Siboga" did not obtain any species of Chasmocarcinus. 



2) Ann. Sc. Nat. (9), t. 4, 1906, p. 298. Founded on the species P. curtipcs Nobili (pi. 8, f. 7). Hab. Red Sea. 



3) Fauna and Geography Maldive and Laccadive Arch., v. I, 1903, p. 430. Based on the oply species, S. laevis (I.e. p. 43«, 

 textfig. 112), which inhabits Hulule, Male Atoll. 



4) Literature and description of the only known species, Rh. gracilipcs Stimpson: Rathbun, K. Dansk. Vid. Selsk. Skr., 

 7. Raekke, Afd. 5, nO 4, 1910, p. 342, textfig. 27. Alcock (Journ. As. Soc. Bengal, v. 69, prt 2, 1900, p. 322) approaches this genus to 

 Typhlocarcinus and MiERS (Rep. "Challenger", Brachyura, 1886, p. 235, note) to Ceraloplax. Hab. Chinese Seas and Gulf of Siam. 



53 



