ISOPODA OF THE ' LIGHTNING ' AND OTHEE EXPEDITIONS. Ill 



Genus 12. Tanaella, Norman & Stebbing. 

 1. Tanaella unguicillata, Norman & Stebbing. 

 Hab. North Atlantic ; abyssal. 



Genus 13. Anarthura, G. O. Sars. 

 1. Anarthura simplex, G. O. Sars. 

 Hab. Norway. 



Very few members of this family have as yet been noticed beyond the seas included 

 in the North Atlantic ; and when we see what Prof. G. O. Sars has clone in Norway, 

 we cannot doubt that a large number of forms remain to be disco-vered in British 

 seas ; indeed our own collections contain much material which awaits examination. 



Genus 1. Alaotanajs l , n. g. 



Animal elongated ; carapace narrowed in front, without distinct ocular lobes. Pleon 

 not wider than perseon, consisting of six segments, the first five subequal ; the last 

 usually more or less shield-shaped. No eyes. 



Upper antennae in female with three-jointed peduncle and flagellum of several 

 joints ; in the male flagellum furnished with tufts of sensitive cilia. 



Mandibles strong, apices strongly toothed, molar process large and strong. 



Maxillipeds present in the male. 



Gnathopods in female of the usual form, but strongly built, the hand more or less 

 twisted, the thumb toothed on the inner margin ; in male greatly developed, in form as 

 in Leptochelia ; hand very large, oblong, finger and thumb meeting only at the nails, the 

 inner margins of both bearing strong, blunt teeth. 



Perseopods spinous, the spines complex, and varying greatly in structure in the dif- 

 ferent species, thus affording excellent diagnostic characters. 



All segments of the pleon developed, and furnished with ciliated pleopods. 



Uropods two-branched, inner branch long and multiarticulate (8-9-jointed in the 

 species known) ; outer branch 2-jointed. 



Marsupial pouch composed of eight lamellae, which are attached to the first four free 

 segments of the body. 



The species which belong to this genus are among the largest known forms, and live 

 in the abyss of the ocean in from 370 to 1750 fathoms. 



1. Alaotanais sekeatispinosus, n. sp. (Plate XXIII. fig. i., Plate XXIV. fig. r.) 

 Head with a small rostrum, and forming with the coalesced first perseon-segment a 

 rather elongated carapace, widest in the middle, with the coxal regions of the first 



: a\a6s, blind, and Tanais. 



2s 



