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



of the buccal area, aud partly covering with its sharp posterior edge the masticatory parts 

 of the mandibles. 



The posterior lip (PI. VIII. fig. 5) consists of two membranous and somewhat 

 expanded lobes, connate in the greater part of their length, and exhibiting anteriorly a 

 fringe of delicate cilia. 



The mandibles (PI. IV. fig 4, M; PL VIII. figs. 2, 3) are strongly developed, with the 

 body evenly arched externally, and navicular in form. The cutting edge is armed with 

 strong dentiform projections of a somewhat irregular form , and exhibits in its posterior part 

 a distinctly fluted molar surface. As is usually the ease, the armature is somewhat unequal 

 on the right and left mandibles (PI. VIII. fig. 2). The palp is rather large, densely setose, 

 and consists of three joints, the first quite short, the second comparatively elongate aud 

 strongly compressed, the last rather narrow, and provided along the inner sharp edge, 

 almost throughout its whole length, with a dense fringe of delicate spines, disposed in a 

 pectinate arrangement, besides which it has a row of fine bristles (see fig. 3). 



The first pair of maxilla? (PI. VIII. fig. 6) exhibit, as in Lophogaster, two incurving 

 masticatory lobes, of which the outer is the larger, and armed at the truncated apex with 

 short spines, whereas the inner lobe is more membranous in structure, and densely beset 

 with ciliated bristles. These maxillae, however, are readily distinguished by the presence, 

 on the outer side of the basal part, of a distinctly developed two-jointed palp, which, 

 contrary to what is the case in other Podophthalmia, is bent directly backward, so as to 

 project into the branchial cavity, thus accjuiring at the first glance the appearance of an 

 epignath. Both joints of this palp are beset with long aud thin bristles, of which more 

 especially those attached to the ovoid terminal joint are of very considerable length; all 

 these bristles are armed at one of their edges with fine spinules. Regarding the function 

 of this very peculiar palp, it certainlj- may be deemed similar to that observed in the 

 corresponding part of Cumacea and the cheliferous Isopoda, viz., to cleanse the branchial 

 cavity from foreign particles. 



The second pair of maxillae (PI. IV. fig. 4, iif; PI. VIII. fig. 7) are rather large, 

 expanded into lamellse, aud exhibit exteriorly at the base a very consj^icuous mamilliform 

 prominence {x), within which, in spirit specimens, is observed an opaque, finely granular 

 matter. As stated l)y the late Dr. v. Willemoes-Suhm, this prominence in fresb specimens 

 is vividly coloured, and has been regarded liy that author as a kind of visual organ 

 (" accessory eye ") ; hence the generic denomination (TiiathopJiausia. I have, however, 

 failed to trace any refracting elements within this prominence, and hence am in- 

 clined to regard it rather as a kind of phosphorescent organ. The basal part sends oft' 

 internally, as in Lophogaster, two masticator}^ lobes, pointing obliquely forward, of 

 which, however, the anterior is deeply cleft, almost to the base, forming two very 

 narrow lappets, provided, in addition to the usual apical spines, with a transverse row of 

 stiff bristles at some distance from the apex. The posterior masticatory lobe is rather 



