1396 THE VOYAGE OF H.M.S. CHALLENGER. 



distinctly marked ; this pair deeper behind than in front. First joint of the limb, as in 

 all the limbs of the perason, broadly dilated, with a large space left free from muscles, the 

 lower part of the front of the joint in the first four pairs and the corresponding hinder 

 part in the last three being channelled; in the first gnathopods this joint is most dilaterl 

 at a little distance from the base; the apex of the hind margin has three or four spines ; 

 the second joint broader than long, with six or seven spines round the hinder apex ; the 

 third joint rather longer than the second, with a dozen spines round the distal margin 

 where it projects behind the wrist ; the wrist widening distally, longer than the hand and 

 much broader, with three spines on the front apex, one on the margin a little higher up, 

 three or four groups on the hind margin, and others on the surfaces adjoining it, the distal 

 margin which projects behind the hand being set with about a dozen spines ; the hand 

 having spines singly or in pairs at nine points of the slightly convex serrate front 

 margin, others on both surfaces, the hind margin straight, pectinate, carrying five small 

 spines ; the finger little curved, finely pectinate nearly to the tip, more than half the 

 length of the hand. 



Second Gnathopods similar to the first but longer. Branchial vesicles of great size, 

 fully as long as the first joint and much broader. The front margin of the first joint 

 nearly symmetrically convex, so that the greatest breadth of the joint is near the middle ; 

 there are eighteen or more spines round the distal margin of the third joint, which 

 projects behind the wrist as in the first pair, but is longer than there ; the wrist is 

 longer than in the first pair, narrower at the base but distally wider, and a little 

 produced downwards, similarly armed, the distal margin in both cases having some 

 fine pectination ; the hand is a little longer and narrower, with fewer spines than in 

 the first pair, otherwise similar, as is also the finger. The spines which have been 

 mentioned have in most or all cases a delicate feathering on parts of two edges ; the 

 pectination is not uniform throughout, but for the most part consisting of two or three 

 little points alternating with one that is larger. 



First Pergeopods. — Front margin of the side-plates more flattened than in the 

 preceding pairs. Branchial vesicles large like the preceding and following pairs. The 

 first joint rather longer than in the second gnathopods, of the same breadth, but 

 broadest below the centre, and with the muscles running up nearer to the base ; there 

 are six or seven little spines distributed along the hind margin, and three at its 

 apex ; the second joint is a little longer than broad ; the third is shorter than the fourth, 

 with a scarcely perceptible pectination of the hind margin ; the fourth is much shorter 

 than the fifth, but somewhat wider, with three little distant spines on the hind 

 margin, and some slight pectination about its apex, which is in no way produced, but 

 projects behind the fifth joint ; the fifth joint narrow, curved, its concave hind margin 

 minutely pectinate, the pectination becoming a little stronger round the apex ; the 

 finger very short, not a quarter the length of the fifth joint, apparently quite smooth. 



