REPORT ON THE CRUSTACEA MACRURA. 409 



The ultimate pair, which helps to form the rhipidura, is longer than the sixth somite 

 of the pleou ; the outer plate is narrow and has the external margin armed with a small 

 tooth, about a third from the apex, beyond which it is fringed with ciliated hairs, as is 

 also the inner plate. 



Length, 10 mm. (0"4 in.). 



Habitat. — The North Atlantic Ocean. 



Observations. — This species corresponds very closely with Sergestes oculatus, Kroyer; 

 the chief differences are that the outer margin of the rhipidura is armed with a tooth 

 one-third distant from the apex, while in Sergestes oculatus it is smooth, and that the 

 tilth somite has a tubercular, small-toothed prominence on the dorsal surface. Sergestes 

 parmdens also possesses a close resemblance to this species, and demonstrates the 

 affinity that these species have to one another, although they possess certain differential 

 features that are characteristic of specific distinction. 



Sergestes jxirvidens, n. sp. (PI. LXXIV. fig. 3). 



This species corresponds generally with the preceding ; but instead of having only 

 the fifth somite elevated to a dentate protuberance, there is one on the fourth, while the 

 fifth bears a very minute tooth, as does also the sixth, which has the sides proportionately 

 deeper than the preceding somites. The scaphocerite, instead of being rounded at the 

 apex, narrows to a sharp tooth that arms the outer margin at the apex. The second 

 pair of gnathopoda is wanting, but the pereiopoda, all of which are preserved, are long 

 and slender, and correspond with those of Sergestes oculatus. The first pair (fig. 3, k) 

 is furnished with distinct prehensile hairs situated near the ultimate articulation. 



The outer plates of the rhipidura are much longer than the inner, and are fringed 

 on both sides with fine hairs ; the outer margin is not armed with a tooth as in Sergestes 

 ovatoculus, but it is represented by an obtuse angle, about a fourth of the distance from 

 the base, and defines the limit at which the marginal hairs begin. 



Length, 9 mm. (0-36 in.). 



Habitat. — The tropical part of the Atlantic ; Pacific Ocean, north of the Sandwich 

 Islands ; off Sydney and Wellington, Australia. 



Observations. — Specimens of this species or variety were taken during the passage 

 from Teneriffe to St. Thomas ; Sergestes ovatoculus was taken in the North Atlantic, 

 June 14, 1873, and therefore near the same place ; and Sergestes oculatus was taken 

 among the Gulf-weed, and so far as geographical distribution is concerned, the Atlantic- 

 habitats of all these species are within the same region. 



Kroyer has made the existence and position of the tooth on the outer margin of the 



(ZOOL. CHALL. EXP. — PART LII. 1886.) 1 " •"'- 



