52(3 THE VOYAGE OF H.M.S. CHALLENGER. 



distally, fringed with long hairs, and produced to a long and flat rod-like appendage of 

 great tenuity and fringed with ciliated hairs. 



The first pair of gnathopoda is subpediform, short, robust, with the distal joints 

 reflexed, and carries a basecphysis. 



The second pair is pediform, long, robust and terminally pointed, without a dactylos. 



The first pair of pereiopoda is asymmetrical ; the appendage on the right side is robust 

 and chelate ; that on the left is also robust but simple. The second pair is similar in 

 form but different in length. That on the left side is short, that on the right is long, 

 and both have a long and slender multiarticulate carpos. The posterior three pairs of 

 pereiopoda are long, slender and simple, the carpos being as long as the meros and ischium 

 combined, and terminate in a slender, sharp, smooth dactylos. 



The pleopoda are biramose, and the terminal pair, which helps to form the rhirjidura, 

 has a diaeresis on the outer branch. 



The branchiae I have not examined in the only specimen in the collection, but in 

 Nika edulis, from the southern coast of England, in my own collection, there are five 

 pleurobranchiae, which are suspended near the upper extremity of the chamber, but no 

 other plume or mastigobranchial plates ; their disposition is shown in the following tabular 

 arrangement : — 



Pleurobrancbi;e, . . . 1 1 1 1 1 



Arthrobranchia 1 , . . . 



Podobranchiaa, . . . 



Mastigobranc-hia-, . . . 



h i k 1 m n o 



Being unwilling to injure the only specimen in the collection, I have taken the figures 

 of the different parts separately from a British specimen, which appears to differ in little 

 else than size from that brought home by the Challenger, which I have named " p>>'Ocessa," 

 the name given by Dr. Leach to the genus previously to his being aware of Bisso's 

 description. 



The eggs borne by the species of this genus are oval in form and numerous ; they 

 differ from those of most other genera in having the vitellus floating in the centre of a 

 quantity of transparent fluid. 



The form of the brephalos has not been determined. 



Geographical Distribution. — Species have been taken, but sparingly, in various parts 

 of the world. The typical form of the genus was first found by Bisso in the Mediter- 

 ranean in 1816, and by others in the European waters as far north as Scotland. 

 Stimpson records it from Madeira, as well as Nika macrognatha from Hong Kong. Dana 

 describes a species, Nika hawaiensis, from the Bacific ; the Challenger specimen was taken 

 off Amboina in the Eastern Archipelago ; Nika japonica, de Haan, was taken further 

 north, off the eastern coast of Asia. 



