3 o6 DISCOVERY REPORTS 



ventrally in front of the mouth and projects forward below and between the shafts of the antennae. 

 The vertical posterior surface forms an anterior boundary to the oral atrium (Fig. 8). The atrium is 

 bounded laterally by the mandibles, paragnaths and maxillules, and leads antero-dorsally into the 

 oesophagus, which is directed slightly forward and upward. The posterior wall of the labrum usually 

 bulges back to some extent, between the mandibular coxae. It is, however, provided with antero- 

 posterior muscles (Fig. 4 A, a.p.m.), which can draw it forward and so increase the volume of the 

 atrium. It bears a median patch of short, fine, dorsally directed bristles (Fig. 8). Ventrally to the oral 

 atrium, a thin flat surface, with thickened cuticle, extends back horizontally from the labrum like 

 a shelf. This may be termed the labral lamina (Fig. 8, lb. I). Laterally, the posterior edge of this 

 lamina takes the form of comb-like structures. The whole posterior surface of the labrum and the 

 labral lamina is supported by sclerites continuous with the ventral sclerite system of the animal. 



The labrum contains two systems of glands. The anterior of these consists of a number of large 

 unicellular glands, closely packed and running dorso-ventrally. Their openings are evenly spaced over 

 the ventral and lateral walls of the labrum. The openings can only be seen clearly in heavily stained 

 material (e.g. with chlorazol black), when they appear as small crater-like depressions. The second 

 system is a paired compound gland, the two components of which lie partly within the posterior part 

 of the labrum (Fig. 4 A, Ib.g), but extend into the body on either side of the oesophagus. These latter 

 glands open through the posterior wall of the labrum into the oral atrium. 



Fig. 5. C. borealis antipoda. Right mandible from inside, b, basis; b.in, incisor edge of basis; c, coxa; 

 c.tn, incisor edge of coxa; en, endopod; ex, exopod; m, molar surface of coxa. 



Mandibles (Figs. 4, 5, 6) 



Possibly the most interesting feature of the appendages of the Halocyprididae is the structure and 

 articulation of the mandible. Each mandible is biramous, the endopod being large and pediform, the 

 exopod minute. There have been frequent references in the literature to the presence of a gnathobase 

 on its basis as well as on its coxa. This feature is in fact used as a character diagnosis of the whole 

 group. 



The coxa is elongate (Fig. 4 B, c, Fig. 5) and articulates with the side of the body immediately 

 behind the base of the antenna (Fig. 2). The dorsal part is narrow and extends between the base of 

 the antenna and the isthmus which links the carapace with the sides of the body of the animal. The 

 anterior surface of this extension is laterally concave to accommodate the backward swelling of the 

 antennal base. At the apex of the extension there is a cuticular thickening which forms the articular 

 condyle (Fig. 4 B, a.c). Just beneath this condyle a rigid triangular flange (Fig. 4 B, ft) extends 

 forward. Curving downward and inward below the articulation with the body, the gnathobase 



