540 LEPADID.E. 



length of the labrum, and of the space of body between the 

 latter and the lower end of the orifice. The labrum is a 

 very singular part of the mouth from its vast size and out- 

 line : in fig. 8, we have a front view of the mouth, of which 

 the whole upper pointed part consists of the labrum, and 

 hit is the first pair of cirri; in fig. 11, we have a lateral 

 view of the labrum, with the surrounding thin membrane 

 of the body, a — a, still adhering to its edges ; h is the first 

 cirrus on the near side ; m the mandible, a little distorted 

 in order to show its tooth, marking the position of the 

 transverse crest of the labrum and of the orifice] of the oeso- 

 phagus; b b is the medial longitudinal ridge of the labrum. 

 In the Balaninae the labrum forms a mere rim to the back 

 of the mouth, consisting of an inner fold running down 

 the oesophagus, and of an outer fold, both close together : 

 in the Lepadidae the folds are separated, the outer one being 

 swollen or bullate ; and here this structure is carried to even 

 a greater extreme than in Ibla and its allies. The distance 

 between the transverse crest over the oesophagus and the 

 blunt projecting point on the summit of the medial ridge, b b, 

 equals twice the longitudinal diameterof the restof the mouth. 

 The lower margin on each side of the labrum is produced 

 into two projections (fig. 11), the longer one curling round 

 to a point beneath the jaws, with its extremity imbedded as 

 an apodeme. Another very peculiar character in the 

 labrum, prominently noticed by Mr. Hancock, is caused by 

 a longitudinal row, on each side, of closely approximate, long, 

 very finely pointed hairs, which, as already stated, are fronted 

 on the opposed internal surface of the sack by an irregular 

 band of still finer hairs. The surface of the labrum is par- 

 tially covered by minute toothed scales, and these, seen on 

 the longitudinal medial ridge, b b, give it a finely denticulated 

 structure. At each end of the transverse crest which over- 

 hangs the oesophagus, there is a knob, such as occurs on 

 the labrum of every Cirripede. United to these two knobs, 

 which are formed of thick and yellowish membrane, ami 

 springing from the adjoining sides of the mandibles, there 

 are two swellings formed of thin membrane (fig. 8), which 

 occupy the exact position of the palpi, and may be con- 

 sidered as these organs in a rudimentary condition and 

 destitute of bristles. 



