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



outer margin proceeds in a straight line to the distal extremity, the inner margin 

 tapers towards the outer, and the distal extremity is semiarticulated with the rest by an 

 imperfect division, which gives a leaf-like appearance to the part, both margins of which 

 are fringed with hairs, while the inner margin is armed with a small tooth-like projection. 

 The first pair of gnathopoda is seven-jointed and subpediform, the three terminal joints 

 being reflexed and curved backwards, and carries neither ecphysis nor mastigobranchial 

 appendage. 



The second pair of gnathopoda is pediform and four-jointed, the basis and ischium 

 being probably united, and the terminal joint long, narrow, and without a dactylos ; the 

 coxa carries no appendage, but the basis supports a robust ecphysis that is generally 

 attached by a small pedicle. 



The first two pairs of pereiopoda are subequal in form, both are chelate, long, and 

 slender, the hand is narrow, and the fingers long ; both pairs carry a stout basecphysis. 

 The third pair is about half the length of the preceding, it is seven-jointed, carries a 

 basecphysis, is extremely slender, and terminates in a long and styliform joint. The 

 fourth pair is considerably shorter than the third ; it is equally slender, seven-jointed, 

 and carries a basecphysis, the terminal joint being short, compressed, and distally fur- 

 nished with a brush of hair. The fifth pair is longer than the preceding and more robust ; 

 it is seven-jointed, carries a basecphysis, and terminates in a short and broad dactylos, 

 tipped with a brush of hair. 



The first pair of pleopoda has one branch long and multiarticulate, and the other 

 short and membranous. The second and following pairs are subequally biramose, the 

 inner branch being furnished with a long and slender stylamblys, tipped with a bundle 

 of cincinnuli. 



The posterior pair assists in the formation of the rhipidura ; it is biramose, long, 

 foliaceous, and the outer branch is furnished with a diaeresis. 



The branchial arrangement consists of eight plumes, of which the anterior five are the 

 largest. The first two are attached to the membranous articulation of the first pair of 

 pereiopoda, the third and fourth belong to the articulation of the second pair of pereiopoda, 

 and the fifth and sixth to that of the third pair ; the seventh and eighth are not attached 

 to the membranous articulation, but to the interstitial process of the somites of the 

 pereion. The branchial arrangement is represented in the following table : — 



Pleurobranchiee, . . . 1 1 



Artbrobranchiae, . . . 2 2 2 



Podobranchia?, . . . 



Mastigobrancbise, . . . 



hi k 1 m n o 



Observations. — This genus was established by Savigny and placed by him in close 

 relation to the genera Penseus and Sergestes, to the latter of which it possesses a general 



