REPORT ON THE CRUSTACEA MACRURA. 157 



thin chitinous membrane, which appears to be perforated by a small horse-shoe fissure, 

 somewhat out of the centre, and unevenly surrounded by a ring of thickened tissue, 

 that is probably muscular and therefore contractile (see fig. 13, p. 104). The length of 

 the metope is small, and the organs that cover the mouth are produced anteriorly, bo 

 as to reach beyond the anterior margin of the carapace. 



The cheiloglossa or anterior lip is thick and fleshy ; in the centre, anteriorly directed, 

 is a thin, flexible, styliforni process, while the mass of the structure fills up and lies com- 

 pactly in the hollow between the mandibles. The metastoma or posterior lip is likewise 

 a thick and fleshy mass, internally and centrally produced to a small vertical process ; 

 externally and posteriorly the mass overlies the posterior portion of the psalisiform blades 

 of the mandibles, and extends laterally in a slender digital process on each side, and lies 

 in close contact with the mandibles, just where the psalisiform blades are connected with 

 the apophyses. The mandibles consist of a pair of interlocking, scissor-like, serrate 

 blades, differing very little from those in Willemcesia and Polycheles, carrying a two- 

 jointed synaphipod, thickly fringed with hairs, and moved by a long and pointed 

 apophysis, of which the extremity articulates with an underfold of the anterior surface of 

 the carapace. 



The first pair of siagnopoda consists of a double-branched appendage, curved, rigid, 

 and fringed with stiff hairs that become spiniform at the apex of the outer and larger 

 branch ; on the external surface, near the base, there exists a fasciculus of short, thickly 

 ciliated, slender hairs, springing apparently from a common centre. 



The second pair of siagnopoda resembles that of other species ; it consists of two 

 short and small branches on one base, which fold back against a large, flat, foliaceous 

 plate, that is produced anteriorly further than the two previous rami, and posteriorly to 

 an equal extent, and is fringed with cilia that radiate in an anterior direction. 



The third pair of siagnopoda corresponds with that of Polycheles, as shown at 

 p. 135, fig. 32. It consists of three thin foliaceous branches ; the basal one is short, 

 broad, concave, and truncated, and has the margin fringed with hairs ; the middle 

 branch is narrow, and coincides with the curve of the inner margin of the third branch, 

 the corresponding sides being smooth and free from hair, while the outer edge is 

 thickly fringed with short, fine hairs. This and the preceding branch turn outwards 

 and fold back against the next or distal joint, which is much longer and broader than 

 either of the others; it is hollow internally, folding like a leaf upon itself, and this 

 convolution increases considerably towards the apex, where it causes a cup-like appear- 

 ance ; at the outer margin a small bat-shaped flap, thickly and evenly fringed with hairs, 

 is articulated, and acts like a movable valve at the exit of the branchial chamber; from 

 the root or base of the three joints arises a broad, thin, and long membranous plate, 

 the homotype of the mastigobranchia attached to the several pairs of pereiopoda, the 

 epignathite of Milne-Edwards. 



