1'EUUXCULATA POLLICIPES AND SCALPELLUM 



istic of numerous skeletal plates, the peduncle being frequently 



covered with small calcareous pieces, which graduate into the 



larger more regularly placed scutes on the capitulum (Fig. 54). 



The species of this genus, many of which 



are among the largest Cirripedes, are widely 



distributed in the temperate and tropical 



seas, living for the most part attached to 



rocks and often in deep water. P. cornu- 



rajiia occurs off the English and Scottish 



coasts. 



The members of the genus Scalpellum, 

 which is represented by exceedingly numer- 

 ous species in the Cretaceous period, also 

 possess a large number of plates on the 

 capitulum, and often on the peduncle as 

 well, but never so many as in Pollicipes. 

 Although the arrangement of the plates 

 varies much in the different species, we may 



i -i f i i -I c ,, FIG. 54. Pollicipes mitella, 



describe a fairly typical case, that of the x j ( After i> anvin ) 

 common Scalpellum vulgare (Fig. 55, B). 



The valves of the capitulum are held together by the median 

 dorsal piece called the " carina " ; the other unpaired skeletal 

 piece is the " rostrum," in front, just below the place where the 

 valves gape to allow the protrusion of the limbs. The paired 

 pieces receive the names " scutum," " tergum," and " laterals," 

 and the peduncle is covered with rows of small plates. 



The genus Scalpellum is a very large one, and is widely 

 distributed, though at the time at which Darwin wrote only six 

 species were known. The reason for this is to be found in the 

 fact that the great majority of the species live at great depths, 

 so that they remained unknown until the expeditions of the 

 Challenger and other deep-sea expeditions brought them to light. 

 They may affix themselves, generally in considerable numbers 

 together, on branching organisms, such as Corals, Polyzoa, and 

 Hydroids, but often also on empty shells, rocks, and other foreign 

 bodies. The body is colourless or of a pale flesh colour, but 

 a colony of these animals, expanded and drooping in various 

 attitudes from a piece of coral, gives the appearance of some 

 graceful exotic flower. 



Perhaps the most interesting feature of the genus is the 



