578 THE VOYAGE OF H.M.S. CHALLENGER. 



Amjihiplectus, n. gen. 



Carapace without supraorbital tooth, but with orbital and antennal teeth. 



Rostrum slender, minutely serrate. 

 Mandible with Particulate synapbipod and psalistoma, but without molar process. 

 First pereiopod chelate, slender ; carpos not excavate. 

 Second pereiopod chelate ; carpos multiarticulate. 

 Branchiae ten ; mastigobranchia, one. 



Platybema, 1 n. gen. 



Clyclorhynchus, de Haan, in v. Siebold's Fauna Japonica, p. 174 (nom. jprxoc). 

 Rhyncliocydus, Stimpson, Proc. Acad. Nat. Sci. Philad., 1860, p. 96 (nom. prxoc). 



Rostrum orbiculaturn, compressum, membranaceum, oculis et antennis intervenit. 

 Antennas internee bisetaceae, setis brevibus. Max. 5 amm art. secundus articulis 

 duobus ultimis conjunctis eequalis ; art. ultimis spinulosus, penultimo bis longior ; 

 palpi oblongi. Max. 4 arum art. tertius longior secundo ; penultimus abbreviatus. 

 Mandibular incurvatas, corona simplice cylindrica, palpis nullis. Pedes secundi 

 didactyli, tenuiores priniis, carpis brevibus annulatis. Sternum trigonum." (De 

 Haan, loc. cit. Rhyncliocydus (Lysmata) planirostris, 2 de Haan, type. 



Carapace dorsally carinated, produced anteriorly to a large, laterally compressed, deep 

 rostrum, which projects below the level of the dorsal ridge and is inserted between the 

 antennas. Pleon generally, but slightly, compressed laterally, having the lateral coxal 

 plates largely developed. 



Ophthalmopoda short. 



First pair of antennae short, the peduncle not reaching to the extremity of the 

 scaphocerite; flagella two, short, extending but little beyond the extremity of the rostrum. 



Second pair of antennae having a short and broad scaphocerite that narrows towards 

 the extremity, is armed with a small tooth on the outer margin and fringed with long 

 hairs on the inner, and does not reach beyond the extremity of the rostrum ; flagellum 

 about half the length of the animal. 



Mandibles short, strong, cylindrical, without a psalisiform process or synapbipod. 



First pah' of gnathopoda six-jointed. Whether the coxa carries any rudiment of 

 a branchial plume or not I have not determined. The basis carries a long and robust 

 two-jointed ecphysis ; the other joints are short, the carpos is sinuous and partially 

 encroaches on the propodos, which articulates against the anterior margin in its entire 

 length, and has the margin armed with long, curved, ciliated spines. 



1 n'hxTvi, flat, fSyftct, rostrum. 



s Hiiyolyte planirostris, de Haan, in v. Siebold's Fauna Japonica, Crust, tab. xlv. fig. 7. 



Lysmata planirostris, loc. cit., tab. 0. 



Cyclorhynchus planirostris, loc. cit., p. 175. 



