296 GENUS — POLLICIPES. 



on the peduncle, formed when the specimen was young, 

 are smaller than the upper scales ; the lower scales 

 are separated from each other by wide interspaces of 

 membrane, owing to the continued growth of the pe- 

 duncle by the formation of new layers of membrane, 

 and the disintegration of the old outer layers. Each 

 scale is invested by tough membrane (or has been, 

 for it is often abraded off), in the same manner as the 

 valves ; each is furnished with one or more tubuli, 

 in connection with the underlying corium. In P. sertus 

 and P. spinosus, the scales are small, spindle-shaped, 

 and not of equal sizes, and the rows are distant from 

 each other, so that their alternate arrangement is not 

 distinguishable; in these two species, new scales are formed 

 round the summit of the peduncle, and the growth of 

 each is completed whilst remaining in the uppermost 

 row; but, besides these normal scales, such as exist in the 

 other species of Pollicipes and in Scalpellum, new scales 

 are formed in the lower part of the peduncle, which 

 are generally of very irregular shapes, are often larger 

 than the upper ones, are crowded together, and some- 

 times do not reach the outer surface of the membrane. 

 This formation of scales in the lower part of the peduncle, 

 independently of the regular rows round the uppermost 

 part, is perhaps a feeble representation of the calcareous 

 cup at the bottom of the peduncle in the genus Lithotrya. 

 The prehensile antennas will be described under P. cor- 

 nucopia. 



Size. — Most of the species are large: and P. mitella 

 is the most massive of the Pedunculated Cirripecles. 



The Mouth is not placed far from the adductor muscle. 

 The labriun is highly bullate. The mandibles have either 

 three or four main teeth (PL X, fig. 1), with often either 

 one or two smaller teeth inserted between the first and 

 second. The maxillae (PI. X, figs. 13, 14), have their edges 

 either straight and square, or notched, or more commonly 

 with two or three prominences bearing tufts of finer spines. 

 The outer maxillae (fig. 17) generally have a deep notch 



