202 



Ostracotheres H. Milne-Edwards. 



1853. Ostracotheres H. Milne-Edwards. Ann. Sc. Nat. (3), t. 20, p. 219. 

 1906. Ostracotcres Nobili. Ann. Sc. Nat. (9), t. 4, p. 299. 



The only difterence between this genus and the preceding consists in the complete 

 absence of the dactylus of the external maxillipeds. 



Milne-Edwards enumerated 3 species, 2 of which are now considered identical. Only 

 in recent years Nobili added 2 new species. Except a single record from Mauritius all specimens 

 came from the Red Sea. 



Baker in 1908 described two new species of '^ Pinnotheres" from the South Australian 

 coast, P . Jiolothuriensis ^) and P . subglobosa "), which species certainly do not belong 

 to PinnotJieres^ as the dactylus of the external maxillipeds is entirely absent. 

 As the propodus of these maxillipeds is much widened distally, especially in P . holothuriensis^ 

 there is perhaps a greater affinity to Cryptophrys than to Ostracotheres, though the distal 

 margin of this propodus is not obliquely-truncate, but rounded, as in the latter genus. 



There is yet another species of Ostracotheres, which lives on the west coast of South 

 America, viz. O. polittis S. J. Smith '), which much resembles O. cynthiae Nobili by the dactyli 

 of the last pair of legs being longer than those of the preceding pairs, but differs by the carapace 

 being distinctly broader than long, by the last pair of legs being much more slender than the 

 preceding pairs, and also by its habits, O. cynthiae \\v\x\^\x\ Ascidians, O. politus\x\ Lamellibranchs. 



Leaving for the present the Australian and West American species aside we may discri- 

 minate the species of Ostracotheres by means of the following key: 



1. Dactyli of walking legs all of subequal length. ... 2 

 Dactyli of walking legs unequal, those of last pair slightly 



the longest, nearly straight. Carapace as broad as long, 



in cT subcircular, in 9 quadrangular O. cynthiae Nobili 



2. Breadth of carapace \^\.^ times its length. Propodus of 



ext. maxillipeds not longer than carpus O. affinis H. Milne-Edwards *) 



Breadth of carapace scarcely e.xceeding its length . . 3 



3. Carapace quadrangular. Front and ext. maxillipeds gla- 



brous. Fingers of chelae hollowed at tip . . . . . O. spondyli Nobili "') 

 Carapace subcircular. Front pubescent, as are also the ext. 



maxillipeds on their outer surface. Fingers of chelae acute O. tridacnae (Rüppell) = 



O. savignyi (H. Milne-Edwards ") 



i) Transact. Roy. Soc. South Australia, Adelaide, v. 31, p. 177, pi. 23, f. 3. 



2) L.c, p. 179. 



3) Transact. Connecticiit Ac, v. 2, 1870, p. 169; Lenz, Zool. Jahrb., Syst., Supplementbd 5, 1902, p. 765, pi. 23, f. 9; 

 Rathhun, Proc. U.S. Nat. Mus., v. 38, 191 1, p. 545, pi. 43, f. 3. Hab. coasts of Peru and Chile. 



4) Ann. Sc. Nat. (3), t. 20, 1853, p. 220, pi. 11, f. 11; NoiULi, Ann. Sc. Nat. (9) t. 4, 1906, p. 300. Hab. Mauritius and Red Sea. 



5) Buil. Mus. Paris, t. II, 1905, p. 164. Hab. Persian Gulf. 



6) Literature: NoBiLT, Ann. Sc. Nat. (9), t. 4, 1906. p. 299; Stekbing, \\m. S. A. Museum, v. 6, 1910, p. 331; Lenz et Stkunck, 

 Deutsch. Südpolar-Exp. 1901 — 1903, Bd 15, 1914, p. 283. It is remarkable that this rather common species of the Red Sea is recorded 

 by Krauss from Natal and by Strunck from Simons Bay (Cape Region). The Leiden Museum contains two specimens ((ƒ and 9) 

 coUected by Mr. J. A. Kruyt in 1881 at Djeddah. 



114 



