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



each gradually becoming less prominent until in the fifth it exists as a thin, pointless 

 plate. 



The ophthalmopoda are rather small and round, and rest in a concave depression in 

 the upper surface of the first pair of antennas, where they are protected by a thin stylo- 

 cerite. 



The first pair of antennas (fig. 2b) is short, the extremity of the peduncle reaching 

 scarcely beyond the level of the fronto-lateral angle of the carapace. The first or coxal 

 joint is furnished on the outer side with a sharply pointed stylocerite, the inner margin 

 of which is fringed with fine cilia, while a fasciculus of a few long hairs springs from 

 the surface, and surrounds the eye ; the second joint is longer than the first and is pro- 

 duced to a point at the outer distal angle ; the third is shorter than the second, and is 

 armed with a short tooth on the outer margin. The flagella are unequal ; the outer or 

 primary, which is scarcely twice as long as the peduncle, is very robust, flattened, rapidly 

 tapers to a fine extremity, and is abundantly furnished with membranous cilia. The inner 

 or secondary flagellum is more slender and longer than the primary, and fringed with 

 numerous simple hairs. 



The second pair of antennae (fig. 2c) has the last joint of the peduncle long and the 

 other joints short ; the scaphocerite, which is almost circular, being as broad as long, is 

 furnished with a small tooth on the distal extremity of the outer margin ; the inner 

 margin is fringed with long hairs, and the distal surface minutely pilose. The flagellum 

 is about half the length of the animal and is thickly studded with minute, short, 

 stiff, curved spinules. 



The second pair of gnathopoda (fig. 2i) is long, slender and four-jointed, reaching 

 beyond the extremity of the first pair of antennae, and carries a short biarticulate basec- 

 physis. 



The first pair of pereiopoda (figs. 2k, 2k") is long and robust and approximates in form 

 to that of Crangon vulgaris. The anterior margin of the propodos (fig. 2k") is more 

 oblique than in Crangon, the incisive margin being thin, smooth, and fringed with hairs 

 at its base ; the dactylos is sickle-shaped. The second pair of pereiopoda (fig. 3, I) is 

 shorter, being about two-thirds the length of the first ; it is chelate and the fingers of 

 the chela impinge only at their apices. The third pair of pereiopoda (fig. 3, m) is styliform, 

 slender, and twice the length of the second, reaching beyond the extremity of the first. 



The first pair of pleopoda (fig. 2p) has the rami unequal and foliaceous, and the 

 margins fringed with hairs ; the others (fig. 2q) have the rami equal and foliaceous, and 

 carry a single stylainblys on the inner margin. 



The posterior pair of pleopoda, forming the outer plates of the rhipidura, is long and 

 narrow, but scarcely so long as the telson ; the outer branch is armed with a small tooth 

 on the outer distal extremity but has no diaeresis ; and the inner margin is fringed with 

 hairs. 



