MANDIBLES AND MAXILLA 295 



lobes with finely ciliated edges. Between the lips the hard 

 and strong mandibles make their dentate cutting edges 

 meet. They have no ' palp.' The left mandible, and rarely 

 also the right, has a secondary plate on the inner side. 

 The molar tubercle is generally a long and strong process 

 at right angles to the body of the mandible, with a denti- 

 culate crown ; but in one family, the Campylaspidas, the 

 process is thin and stiliform. Between the cutting edge 

 and the molar there is usually a row of spines. It is, 

 however, distinctive of one family, the Leuconidge, that this 

 spine-row is absent, being represented only by a couple of 

 setae. The first maxillae may be roughly described as con- 

 sisting of an inner and outer plate, each tipped with spines, 

 and of a backward directed ' palp.' The inner plate is an 

 expansion of the first joint, and the outer plate an expan- 

 sion of the third, the small second joint between them 

 being very little conspicuous. Close to the base of the 

 outer plate on its outer side is placed the ' palp,' which 

 may be the fourth joint of the endopod turned back to serve 

 a particular purpose. It is very movably articulated, and 

 ends in one or two long setae. Its function is reasonably 

 supposed to be that of clearing the branchial sacs from any 

 obstructive particles which might be brought in along with 

 the water introduced by the action of the breathing ap- 

 paratus. In the genus Pa/rala/mprops, however, this ser- 

 vice must be dispensed with, for there the ' palp ' does not 

 exist. 



The second maxillae are analysed by Hansen into four 

 joints, of which the second is very large, having a row of 

 setae on the inner margin and a small terminal plate tipped 

 with setae. The third and fourth joints have also each a 

 similar small terminal plate, and to the outer rim of the 

 third joint is attached a thin plate with curved margin, 

 which is explained to be morphologically a weaker develop- 

 ment of the fan as it occurs in the Mysidse. 



Upon the next pair of appendages, the first maxilli- 

 peds, the interest of the Cumacean group is above all con- 

 centrated, for these present features that are unique among 

 the Crustacea. The endopod or limb-like portion of the 



