538 LEPADID.E. 



from the lower end of the orifice of the sack ; hence the 

 labium and whole mouth is placed quite remarkably near 

 the upper (or carina!) end of the orifice. This upper end of 

 the orifice, I may remind the reader, is homologically the 

 posterior end of the general covering or carapace, and all that 

 portion of the whole animal (as the sectional figure, 5, stands) 

 below the lower margin of the labrum, on the rostral or 

 ventral surface, is formed by the three anterior segments of 

 the head. The main part of the body, carrying the mouth, 

 is formed by the great development of that segment of the 

 thorax which bears the first pair of cirri (7t), here closely ad- 

 pressed, as usual, to the sides of the mouth. The lower 

 portion of this segment forms the prosoma («'), and has the 

 characteristic outline, but is not much developed. On each 

 side of the prosoma an oval space of membrane is yellowish 

 and is thickened, and so gives support to this part of the 

 body. The five succeeding thoracic segments, which ought to 

 carry the five succeeding and posterior pairs of cirri, are 

 together of very small size (as in Ibla), in comparison with 

 either the prosoma, or the whole anterior part of theanimal. 

 The segment {k) which should have borne the second pair of 

 cirri, is considerably longer than the following segments, and 

 is at the same time less distinct, owing to an oval convex shield 

 of thickened membrane on the sides, not extending the whole 

 length of the segment, thus causing two transverse creases, 

 which, when the thorax is contracted, appear like two ad- 

 ditional segments. Had this segment borne cirri, they 

 would have stood, as in Ibla, at a considerable distance 

 from the first pair. The segments (/, />/) which should have 

 borne the third and fourth pairs of cirri are like each other, 

 except that the former is rather the longest. The mem- 

 brane covering all the thorax is surprisingly thin ; and at 

 the articulations, which are straight and transverse, is 

 deeply folded, so that the thorax must be highly extensible, 

 to a degree which I have not seen equalled in any Cirripede 

 except in the males of Scalpe/lum vulgare and ornatum. 

 The thorax is represented as somewhat extended in fig. 5. 

 This part of the thorax is amply furnished with striated 

 and stria3-less muscles for its retraction and protrusion, and 

 for lateral movements. The segment (m) which should 



