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



the sex depends upon the presence of what I believe to be a pair of uvigerous lamellae 

 attached near to the bases of the third pair of thoracic appendages. One of them is shown in 

 fig. 10 ; it is a thin plate projecting inwards from the surface of the thorax, just inside of 

 the articulation of the appendage ; the shape of the lamella can be understood by an inspec- 

 tion of the figure ; it is somewhat concave anteriorly and convex inwards ami posteriorly ; 

 along the margin are a series of grooves giving to this region a tessellated appearance. I 

 could not find any trace of an ovigerous lamella on any other segments of the body ; the 

 remarkable disposition of the ovigerous lamella in Ta/nais willemcesii from Kerguelen, 

 described by the late v. Willemoes-Suhm, and more recently by Studcr, prepares us for 

 abnormalities in this respect in Isopoda from that region of the globe; it may be, 

 however, that the other ovigerous lamellae have not yet appeared owing to the immature 

 condition of the specimen, though this is not generally the case with Isopoda ; it is also 

 possible, but not probable, that this structure does not correspond with the ovigerous 

 lamellae. 



The antennuhs (fig. 2) are articulated with the head by a stout basal joint of cylindrical 

 form; the dorsal region of the first joint is prolonged some way beyond the articulation 

 of the next joint, -which is considerably smaller ; the fourth and fifth joints are very small. 

 The flagellum is long, about three times as long as the basal region of the antennule ; it 

 appears to be perfectly smooth proxknally and gradually becomes more and more ringed, 

 until it is evidently made irp of a number of separate joints ; the sensory filaments are 

 restricted to the distal region of the appendage. 



The antenna;, as already observed, are remarkably long even for a genus which is 

 characterised by the length of the antennae ; the proximal joints areas usual extremely 

 short and subequal in length. The fifth joint measures alone no less than I 5 mm. Onlv 

 the distal one-sixth of the joint is occupied by the muscles, which effect the movement 

 of the succeeding joint (see fig. 3); the latter is comparatively very short; the long 

 flagellum measures in the example before me 17 mm., but the extremity is evidently lost, so 

 that it is impossible to calculate how much longer it was during life ; the flagellum shows 

 traces of division into separate joints, which appear to be very long. 



The mandibles differ somewhat from the typical form of the mandibles of other 

 Munnopsids. The specimen itself is labelled in the handwriting of v. Willemoes-Suhm 

 as a doubtful Munnopsid, and it is possibly these very appendages, which are conspicuous 

 and readily to be made out, which led v. Willemoes-Suhm to hesitate before including 

 the species in the genus Munnopsis or its immediate allies. 



In fig. 8 of PI. XIII. I have figured one of the mandibles; it is a conical stout 

 appendage slightly curved inwards towards its fellow; the biting edge is prolonged into 

 a stout tooth distinguishable from the rest of the appendage by its yellow colour, behind 

 which are traces of other teeth in the way of slight crenulations of the margin ; the 

 asymmetry between the two mandibles is not very striking : the most remarkable fact, 



