1474 THE VOYAGE OF H.M.S. CHALLENGER. 



vesicles of great size. The first joint very similar in shape to that in the second 

 o-nathopods, but with the muscles more strongly developed, the greatest breadth some 

 distance above the distal end, the sides smooth ; the second joint longer than broad ; the 

 third joint longer than the fourth or fifth, widest not far from the base, the front margin 

 convex, the hinder slightly concave ; the fourth joint a little curved, wider than the 

 fifth, but scarcely so long; the fifth having some fine denticulation at the hinder apex; 

 the finger curved, very short and thin, at the base narrower than the fifth joint, and 

 almost immediately abruptly narrowing. 



Second Perasopods very similar to the first, but with the second, third, fourth, and 

 fifth joints considerably longer. 



Third Perasopods. — Side-plates deeper behind than in front, with a strong triangular 

 tooth on the inner side at about the middle of the lower part, directed backwards. 

 Branchial vesicles not so large as the first joint. The first joint more than twice as long 

 as broad, the hind margin evenly convex, the front sinuous, the chief concavity being 

 below the centre, the distal part curling round below the second joint ; the plate is 

 narrowest at the two extremities, having its greatest width near the centre ; the 

 remaining joints folded back against its inner surface do not reach the top ; the second 

 is short, the third longer than the fourth, the fifth longer than either, having its 

 convex hind margin produced into a minute spike ; the front margin is minutely 

 pectinate in the third, fourth, and fifth joints ; the finger is rather longer than in the 

 preceding feet, with the hind margin a little jagged. 



Fourth Perzeopods. — The side-plates with the hind margin longer than the front, the 

 two nearly parallel. The branchial vesicles broad, not nearly so long as the first joint. 

 The first joint larger than in the preceding pair, the lower part a little narrower than 

 the upper, the upper part of the hind margin strongly convex, the lower half where the 

 margin is double nearly straight ; near the lower end of the convex part there is a very 

 small slit on the outer surface ; the front margin is for the most part concave, the lower 

 margin slightly oblique, rounded in front ; a strip along the front and lower margins has 

 a striated appearance, observable also round much of the border of the first joint in the 

 third peraeopods ; the remaining joints together equal about one-third the length of the 

 first ; the second joint short, attached some way up and within the hind margin of the 

 first ; the third joint very long, the front margin a little longer than the hinder, forming 

 a small apical triangle, and strongly pectinate almost from the base to the tip ; the 

 fourth joint narrower than the third and little more than half its length, similarly 

 pectinate, narrowing distally ; the fifth joint, which is the last, slender, acute, more than 

 half the length of the fourth, finger-like. 



Fifth Perseopods. — Side-plates small, triangular, deeper than broad, the apex not 

 reaching nearly as far as the lower border of the preceding pair. The limb consisting of 

 a single joint, laminar, almost crescent-like, bending across the top of the preceding limb 



