530 Orchestoidea, ürchestia 



Body smooth. Side-plate 5 much shallower thau 4^^. Pleon segment ;}, 

 postero- lateral corners quadrate. Eyes rather large, approximate in front. 

 Antenna 1 very sliort, flagellum 3-jointed. Antenna 2 in 9 not half as 

 long as body, flagellum scarcely as long as peduncle, about 16-joiuted. 

 Gnathopod 1 in d as in 9 . Gnathopod 2 in d, 6**^ Joint large, subovate, 

 palm slightly couvex, spinulose, very oblique, 4gfined by a well marked 

 angle but not tootlied, finger elongate. Gnathopod 1 in o longer than 

 gnathopod 2, finger thick, curved, not much shorter than the palmless 

 6*^^ Joint, which in figure appears longer than 5**^. Gnathopod 2 in 9 , 

 ö*'^ Joint with very bulging hind margin, 6^^ with straight front and bulging 

 bind margin, distally narrowly produced much beyond the minute longitudinal 

 finger. Peraeopods 4 and 5 much longer than the preceding peraeopods,. 

 2^ Joint broadly expanded, the rest slender, spinules numerous. Uropod 1 

 rather long, üropod 3 short, ramus as long as peduncle. L. 12 mm. 



Rio Janeiro harbour. 



4. Gen. Orchestia Leach 



1793 [Subgen.J Gammarelhis (part.), J. F. W. Herbst, Naturg. Krabben Krebse^ 

 V.2 p. 106 ! 1802 Talitrus (part.), (Latreille in:) Bosc, Crust., v. 1 p. 78 | 1802 T. 

 (part.), Latreille, Hist. Crust. Ins., v. 3 p. 38 | 1813/14 Orchestia 

 (Sp. un.: 0. Uttorea), Leach in: Edinb. Enc, v.7 p. 402 | 1888 0.» 

 T. Stebbing in : üep. Voy. Challenger, v. 29 p. 602, 1678 | 1890 0., 

 G. 0. Sars, Crust. Norway, v.l p. 24 i 1893 0., A. Della Valle in: 

 F. Fl. Neapel, v. 20 p.494 j 1847 Scamballa (part.), (Leach in MS.) 

 A. White, Criist. Brit. Mus., p. 86 | 1876 Orchestes (non Illiger 1798, 

 Coleoptera!), R. T. Maitland in : Tijdschr. Nederl. dierk. Ver., v.2 p. 11. 



Like Talitrus (p. 524) except that gnathopod 1 (Fig. 93) 



in ö and in 9 is less strongly developed and is subchelate 



instead of simple, while gnathopod 2 in d is powerfully 



subchelate instead of feebly chelate. Antenna 2 in d perhap» 



never attains so strong a development as is met with in 



Talitrus and Talorchestia (p. 543); the maxillipeds seem 



Fig. 93. sometimes to have an obscure rudiment of the 4*^ Joint of 



o. seikirki, $. the palp, and the front lobe of side-plate 5 may be as deep 



nat opo 1. ^g side-plate 4. Tbe notehing of the finger in peraeopod 2 



is seldom so sharp and decided as in Talorchestia. 



Generally distributed in temperate and tropical seas between tidemarks among 

 sea-weed and stones, as distinguished from the sand-dwelling Talitrus and Talorchestia» 

 also found inland at various heights up to 1375 m above sea-level. 



23 accepted and 6 doubtful species. 



Synopsis of accepted species:*) 



i Peraeopod 5 in adult (5, 4th and 5^^ joints strongly 

 incrassated — 2. 

 Peraeopod 5 in adult (^, 4th and 5th joints not strongly 

 incrassated — 6. 



f Gnathopod 2 in (5, palm extremely oblique ... 1. O. mediterranea. p. 531 

 \ Gnathopod 2 in (J, palm not extremely oblique — 3. 



*) Since this table is based upon structures of cJ, the species 22 and 23, of 

 which cj specimens are unknown, are omitted; they differ by the palm of gnathopod 1: 

 feebly developed in 22, 0. parvispinosa p. 541, well developed in 23, 0. montana p. 542. 



