1486 THE VOYAGE OF H.M.S. CHALLENGER. 



Lower Antennse. — Third (first free) joint of the peduncle short, pyriform, greatly dilated 

 near the base, smooth-edged ; the following joints elongate, ciliated, the fourth joint being 

 scarcely as long as the fifth ; the first joint of the flagellum is narrower than the last of 

 the peduncle, but only a little shorter, and the second joint is more than three-quarters 

 the length of the first, the terminal filaments being longer than those on the margin. 



Hie Mouth Organs appear to a great extent to coincide with those which Claus 

 figures for Amphithyrus bispinosus. The palp of the Mandibles is long, the first joint 

 the broadest, long, but a little exceeded in length by the second, the third joint being 

 narrower than the second but as long, with a rounded not an acute tip. The trunk of the 

 First Maxillae is of uniform breadth for some distance, but narrows towards the apex by 

 the inner margin turning obliquely outwards, this inner margin being armed near the 

 apex by two somewdiat curved retroverted teeth ; the Maxillipeds have the inner plate 

 broadly rounded, the distal border smooth, with two embedded spinules at the centre, 

 the outer plate broad, partly folding round the inner and reaching not very far 

 beyond it. 



First Gnathopods. — The side-plates a little produced forwards at the rounded lower 

 angle ; as in many other species of the group the upper boundary of the side-plates is 

 present, but very difficult to j^erceive, which may account for its omission in the figure of 

 Amphithyrus scidpturatus. First joint about as long as the following four joints together, 

 widened nearer to the apex than the base, the muscles running to about the middle of the 

 joint; second joint a little longer than broad, with a setiform spine near the hinder apex ; 

 the third joint broad, rather longer than broad, the hinder apex acute, scarcely produced ; 

 the wrist as broad as the third joint, and with its acutely produced hinder apex equalling 

 it in length, not as in Amphithyrus scidpturatus exceeding it ; just within the acute 

 tip of the triangular apex there is a little spinule ; the hand is about as long as the 

 wrist, but much narrower, the hind margin having a produced apex like that of the 

 wrist but smaller, the front of the hand, however, being produced quite as far as the apex, 

 so that there is a triangular cavity between them over which the small curved finger 

 bends ; the finger has a cilium on or near the inner margin. There are gland-cells 

 observable in the first four joints, and in the second, third and fourth a series of minute 

 ducts appear to connect these with the hind margin. 



Second Gnathopods. — Side-plates deeper than wide, with convex front and concave 

 hind margin. The branchial vesicles large, but not so large as those of the following 

 limb. The first joint a little bent, longer than in the first gnathopods, longer than the 

 rest of the limb ; the second joint longer than broad, with four setiform sj)ines on the 

 hind margin ; the third joint considerably broader and perhaps a little longer than the 

 wrist, with four setiform spines along the hind margin, two or three others probably 

 having been lost ; the wrist, hand, and finger nearly as in the first gnathopods, but the 

 process of the hand does not reach quite so far as the apex of the front ; near the hind 



