10 G. 0. Sårs. 



prominence of the preceding joint, though of rather smaller 

 size, and also 3 simple bristles (see fig. 7). 



Between the bases of the inferior antennæ the anterior, 

 hood-like part of the labrum projects, its posterior part, de- 

 fining the oral aperture in front, occurring rather far back 

 between the mandibular palps and the anterior maxillæ. 

 The oral aperture behind is bounded by the median ven- 

 tral shield, or plastron (see figs. 9 & 15), which is 

 somewhat dilated in front, and produced on each side to a 

 narrow linguiform lobe. Between the latter there are 2 

 strongly chitinous rods armed on their expanded extremi- 

 ties with coarse brown-coloured teeth. 



The mandibles (fig. 10) are very strongly built, each 

 consisting of a highly chitinized body and a well-developed 

 pediform palp. The body extends nearly vertically across 

 the side of the animal, its upper acutely produced ex- 

 tremity being articulated to the inner side of the shell, 

 immediately in front of the adductor muscle. The mastica- 

 tory part is slightly incurved, and meets the corresponding 

 of the other mandible at the oral orifice. The cutting edge 

 is divided into a number of strong denticulated teeth, suc- 

 cessively diminishing in size inwards, and having between 

 them stiff bristles. At the base, outside, this part carries a 

 short seta. The palp is curved downwards just behind the 

 base of the inferior antennæ, and is divided into 4 well- 

 defined joints, the first of which is by far the largest, and 

 exhibits at the posterior corner 2 or 3 strong plum ous setæ 

 curved backwards. To the outer side of this joint a thin 

 branchial plate is attached, extending upwards, and carrying 

 6 densely plumous setæ, 5 of which issue from the tip, the 

 6th from a separate ledge of the anterior edge. The 2nd 

 joint is rather short, and provided both in front and be- 



