2or 



Merus of external maxillipeds suboval, antero-external angle 



not produced. Abdominal segtnents of cf 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 . . . . . Paraselwynia n. g. 



9. Carapace much broader than long 10 



Carapace only a little 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^l„ times the length of carapace Rhizopa Stimpson *) 



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



fiUing up the interspace between the coxopodites of the 



last pair of legs Typhlocarcinus Stimpson 



1) This genus was founded on the species C/i. lypiciis Rathbun (Buil. Lab. State Un. lowa, v. 4, 189S, p. 285, pi. 7, f. 3 — 5), 

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

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

 Bay, Lower Califoinia, and in igoi a fourth species, Ch. cylimiriciis (Buil. l'. S. Fish Comm. for 1900, v. 2, 1901, p. 10, textfig. i) 

 fiom 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. cavima/nis^ 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. (9J, t. 4, igo5, p. 298. Founded on the species P. curtlpes Nobili (pi. 8, f. 7). Hab. Red Sea. 



3) Fauna and Geography Maldive and Laccadive Arch., v. i, 1903, p. 430. Based on the only species, S. laevis (I. c. p. 431, 

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



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

 7. Raekke, Afd. 5, n" 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 Ceratoplax. Hab. Chinese Seas and Gulf of Siam. 



53 



