134 THE VOYAGE OF H.M.S. CHALLENGE K. 



of the flagellurn is a tuft of exceedingly long slender hairs which arc quite twice the 

 length of the whole appendage ; as in other Tana ids there appear to be no auditory hairs 

 upon the last joint of the antennule, and perhaps this fact is in favour of regarding the 

 last joint as belonging to the peduncle and not representing the flagellurn, which in that 

 case would be absent. 



The antennae (fig. 12) are rather shorter than the antennules, but like them appear to 

 consist of only four joints, five being the usual number found in this appendage in other 

 Tanaids. The first joint is wide and flattened, and is prolonged on the inferior surface for 

 some way beyond the articulation of the second joint, in fact, as far as its distal extremity ; 

 the second joint is altogether smaller than the first joint but has the same general form ; 

 it is widened and flattened and projects on the ventral side for a short distance beyond 

 the third joint ; the latter is of about the same length as the preceding joint, but narrow 

 and cylindrical ; the distal joint of the appendage is short and narrows towards its 

 termination. 



A large number (fourteen) of individuals dredged in 2 to 10 fathoms, in Port Jackson, 

 appear to me to be hardly distinguishable from this species, which thus is an example of 

 the very unusual occurrence of a species which is common to very shallow water and to 

 the great abysses ; such instances in the Isopoda are so extremely rare that I am inclined 

 to doubt whether there has not been some mistake made with reference to the specimen 

 alleged to be from Station 246, 2050 fathoms ; at any rate, for the present, it appears 

 necessary to regard the fact of its occurrence in very deep water with a certain 

 reserve. a 



Among the specimens dredged in shallow water at Sydney there are two series of 

 individuals which I imagine to be males and females respectively ; in certain individuals 

 the abdomen is distinctly longer than in others, and as this sexual difference occurs 

 in L&ptognathia it is probably a mark of sexual distinction in the present species; it 

 is the only one, at any rate, that I could detect. There is absolutely no difference 

 in the structure of the antennules; they are perfectly similar in all the fourteen 

 individuals. 



Station 246, Mid North Pacific, July 2, 1875; lat. 36° 10' N., long. 178° 0' E.; 

 depth, 2050 fathoms ; bottom temperature, 35°'l F.; Globigerina ooze. 

 Port Jackson, 2 to 10 fathoms. 



1 It must be remembered, however, that a species of Typhlotanuis, labelled on a slide during the Expedition Gram 

 Station 246, is apparently identical with Typhlotanau kerguelcnensis; hence there is some independent evidence from 

 analogy, in favour of supposing that no mistake has been made with respect to the occurrence of Bathytanais bathybroies 

 in deep water as well as shallow. 



