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



or small joints, armed on the flexor surface with two or three long, strong, distally 

 serrate spines, and several shorter ones (fig. 3, i). 



The first pair of pereiopoda is short, not reaching beyond the distal extremity of the 

 rneros ; it is five-jointed, slender, and furnished with a prehensile brush (fig. 3, h) at the 

 carpal articulation of the meros ; the carpos or terminal joint is more slender than the 

 preceding and is straight. The second and third pairs are long and slender, but not so 

 long as the second pair of gnathopoda, and terminate in small chelae, each finger of which 

 is tipped with a brush of radiating hairs. The fourth pair of pereiopoda is short, about 

 half the length of the third pair, reaching to the distal extremity of the meros, and is 

 fringed on the posterior margin with long hairs. 



The fifth pair is shorter and more slender than the fourth, reaching to about one-half 

 its length. 



The first pair of pleopoda is short and single-branched ; the second is equally short 

 but double-branched ; the three posterior are subequal in length but more robust ; the 

 posterior pair is short and devoid of a tooth on the outer margin of the external plate, 

 which is fringed with a series of small hairs. 



Length, 18 mm. (07 in.). 



Habitat. — The Atlantic Ocean, April 7, 1876. 



Observations. — This species bears a resemblance to Sergestes ancylops, Kroyer, but 

 differs from it in the length and form of the ophthalmopoda, the length and robust character 

 of the second pair of gnathopoda, the shortness of the sixth somite of the pleon, the 

 absence of a tooth on the outer plate of the rhipidura, and in the length of the 

 telson. 



In the middle of the Pacific, north of the Sandwich Islands, several specimens of 

 Sergestes in various stages of progressive growth were taken, and among them was one 

 2 - 5 mm. in length, which agreed with this species in all details, except that it had a long 

 and slender rostrum. Another specimen, 3 mm. in length, differed only in the length 

 of the rostrum, and a third, 4 mm. in length, corresponds with the Mastigopus shown on 

 PI. LXV. fig. 4, with which the two preceding also agree in all details, except in the 

 dorsal teeth on the pleon and in the length of the rostrum, which in the two smaller 

 specimens has a few denticles or teeth towards the extremity. Whether the larger 

 belong to the same species as the two smaller it is difficult to determine, but the resem- 

 blance of the smaller to this species has induced me to draw attention to them in this 

 place. The larger form appears rather to be the young of Sergestes oculatus. 



