the Mouth in Sucking Crustacea. 15 



the maxillipeds at once arrest the attention. The cardo 

 (PI. I. fig. 4 h^ c) is exjjandecl outwards and forwards into a 

 large triangular plate, which covers the root of the second pair 

 of maxillge. The stem is very large, elongated, quadrangular 

 (fig. 4 5, s), its underside sHghtly vaulted; but the lateral 

 or outer portion is boldly arclied upwards, so as to embrace 

 the maxillse of the second pair ; and the upper sm-face of the 

 stem has near the inner margin a thick longitudinal crest 

 fitting so accurately into a depression on the corresponding- 

 side of the middle ridge of the sphenoid plate between this 

 ridge and the maxilla of the second pair, that the stem by 

 these means is kept quite firmly in its position. On account 

 of this crest, the stem appears rather thick when detached and 

 viewed from the side of the inner margin, which latter is quite 

 straight and even, so as to fit in exactly with the correspond- 

 ing margin of the maxilliped on the opposite side, to which it 

 lies close through the whole of its length. 



The five-jointed pa/^;ws of the maxillipeds (^;, fig. 4 V) is 

 of about the same length as the stem. The first joint is very 

 short, and is placed transversely in front of the fore end of the 

 stem, whilst the four following joints form a bluntly pointed, 

 inwardly curved, cup-shaped leaf, which rests on one edge, so 

 that it inclines a little inwards. The upper (and outer) even 

 edge of the leaf fits first into a narrow groove on the inner 

 edge of the stem of the mandible, and then passes round the 

 mandible and lays itself into the bend between the mandibular 

 stem and lobe, whilst the front edge is curved inwards and 

 embraces the corresponding side of the labrum. On the in- 

 ferior margin of the palpus, near the end of the second joint, a 

 couple of small soft hooks are implanted ; and a greater number 

 of such are distributed along the margin and along the outer 

 side of the following joints. They do not, however, appear as 

 hooks, except when viewed from the side, and particularly 

 when the palpus is pressed flat ; but from beneath or from the 

 side, when the palpus is in its natural shape, they are seen 

 fore-shortened, and then appear as a row of short thorns along 

 the margin of the third joint, and as a lump of warts on each 

 side of the labrum. 



In this manner the two leaves formed by the palpi, placed 

 on edge and bending towards each other, embracing some 

 other parts of the mouth, constitute the sides of the sucking- 

 tube. Nevertheless a slit remains between them ; but this is 

 filled up at the bottom by the two very short, conic, com- 

 pressed, brevisetose lobes of the maxillipeds, and, further, in 

 front by the inner lobes of the second pair of maxillge, which 

 will afterwards be described. 



