IV PEDUNCULATA—POLLICIPES AND SCALPELLUM 85 
istic of numerous skeletal plates, the peduncle being frequently 
covered with small caleareous 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- 
copia oceurs 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 
eapitulum, 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 
describe a fairly typical case, that of the ae en a 
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 
