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



Sergestes nasidentatus, n. sp. (PI. LXXII. fig. 2). 



Rostrum produced to a sharp point, and armed on the upper surface with a distinct 

 tooth, a little anterior to the frontal margin. Carapace about one-third of the length of 

 the animal ; dorsal surface depressed, with a groove over the gastric region. 



Pleon with the dorsal margin smooth ; the five anterior somites subequal, lateral 

 margins rounded ; sixth somite longer than the two preceding and rather deeper than 

 the fifth, and postero-dorsally produced to a small tooth in a line with the dorsal 

 surface. 



Telson about one-half the length of the sixth somite. 



Ophthalmopoda long, stout, and clavigerous, about two-thirds the length of the 

 carapace. The ophthalmus is scarcely broader than the stalk, and reaches as far as the 

 first joint of the peduncle of the first pair of antennae. 



The first pair of antennae about as long as the carapace ; first joint as long as the 

 ophthalmopod, second about one-third the length of the first, third subequal to the 

 second ; the primary flagellum is slender, but as it is partially broken off its length 

 cannot be determined. The base is enlarged to a bulb, which has a prominence at the 

 distal extremity. 



The second pair of antennae has the terminal joint of the peduncle cylindrical, and 

 more than half the length of the first joint of the peduncle of the first pair, and supports 

 a scaphocerite that reaches beyond the extremity of the ophthalmopoda, is armed on the 

 outer margin, at a short distance from the apex, with a small tooth, and has the inner 

 margin fringed with long ciliated hairs. 



The first pair of gnathopoda is rather slender, but not to an unusual extent. 



The second pair is slender and long, but not so long as the third and fourth pairs of 

 pereiopoda ; the joints are all subequal, and fringed with rather long hairs, more thickly 

 implanted on the flexible or posterior side than on the anterior. 



The first pair of pereiopoda is not very much shorter than the second pair of gnatho- 

 poda, reaching quite as far as the extremity of the penultimate joint of the latter. The 

 joints are subequal ; there is a prehensile apparatus (fig. 2, k) near the last articulation, 

 consisting of a fasciculus of short, stiff, distally serrate hairs or spines attached to the 

 ultimate, and another bundle of short, stiff, simple hairs, to the penultimate joint ; each 

 set is curved towards the other. Beyond these, a little distance from each fasciculus, are 

 two isolated spines or hairs, that are curved towards each other ; these all meet when 

 the limb is flexed, and form a tolerably efficient prehensile apparatus, which may be 

 of a secondary sexual character. The second and third pairs are long, slender, and 

 fringed with long and delicate hairs, implanted in opposite pairs, and perpendicular to 

 the axis of the limb ; each of those pereiopods terminates in a small chela, the fingers 

 of which are tipped with a small brush of bans. The fourth pair is short, scarcely 



