POLLICIPES SERTUS. 331 



about two segments; basal segments protuberant/ brush- 

 like. Second and third cirri with live basal segments of 

 both rami protuberant and brush-like ; but the anterior 

 rami in both cirri are broader than the posterior rami- 

 Spines on the protuberant segments of both rami of both 

 cirri, coarsely and doubly pectinated. 



Caudal Appendages (PI. X, fig. 19), minute, uniarticu- 

 late, club-shaped, with the enlarged ends directed inwards, 

 or towards each other ; summits sparingly clothed with 

 very short spines. 



Penis, small. 



Affinities. — This species makes a very close approach 

 in the general form and relative sizes of all the valves, 

 and in the variability of the number of the whorls, to 

 P. spinosus; there is a still closer and more important 

 resemblance, in the inequality and manner of growth of 

 the calcareous scales on the peduncle. These species 

 differ, in the colour of the membrane covering the valves, 

 and in the greater development of both rostrum and sub- 

 rostrum in P. sertus. The rostrum of the latter is longer 

 than half the length of the carina, and its inner surface 

 is more than twice as high as wide ; and the sub-rostrum 

 is twice as large as any of the latera, — all points of dif- 

 ference from P. spinosus. 



In the characters of the mandibles, and more especially 

 of the outer maxillae ; in the length of the first pair of 

 cirri ; in both rami of the second and third cirri having 

 their basal segments brush-like, with pectinated spines ; 

 and in the shape of the caudal appendages, there is a 

 close relationship to P. spinosus, and through this species 

 to Scalpellum villosum. In the little prominence of the 

 olfactory orifices, P. sertas differs from most of the allied 

 forms, excepting P. spinosus. In the maxillae having two 

 prominences bearing fine tufts of bristles, in the rough- 

 ened knobs on the prosoma, and in the presence, in some 

 individuals, of two or three whorls of valves under the 

 carina and rostrum, there is a marked tendency in P. sertus 

 to approach P. cornucopia, P. elegans, and P. polymerus. 



