lo dhad 
the Oirripede Genus Stramentum. 75 
no doubt due, in some measure, to additional scales being 
first formed below the carinal and upper lateral valves (see 
under Growth, p. 77), but also to allow sufficient room for 
the animal’s body. 
Of the five rows of scales the three inner series are com- 
posed of nearly equal scales, much elongate transversely, and 
are about as wide as the carinal-latus, upper latus, and 
scutum, below which valves they are situated, so that the 
. lines of junction of the peduncular scales correspond more or 
less with those of the capitular plates mentioned. The 
scales are closely imbricating, the middle series intersecting 
those on either side; and those two series are again in turn 
intersected by the outer subcarinal and subscutal scales, which 
are in line with the middle series ; the much smaller outer 
scales simply meet those on the opposite side of the shell and do 
not overlap or intersect them in any way. Consequent on this 
arrangement of the peduncular scales, alternate whorls are 
formed, one being composed of the large median plates and 
the small outer subcarinal and subscutal scales, making in 
all six rows ; and above and below whorls are formed of the 
two large lateral plates, making four rows. The structure 
and relationship to each other of the peduncle-scales, both 
of the inner and outer surface, is well shown in the specimens 
depicted in fig. 2 of Plates III. & IV. 
The Shell when complete—While Darwin erroneously 
thought that the shell in this genus had a keeled carina and 
rostrum, he was of the opinion that the lateral valves of the 
capitulum, as well as the plates of the peduncle, must have 
been present on both sides of the shell. 
With regard to the lateral capitular valves, excepting the 
carina, decisive proof of their paired nature has been given 
by Whiteaves, for in the holotype of S. canadensis (1889, 
p- 190, pl. xxvi. figs. 4, 4a) the upper lateral series of valves 
has been either partially or completely broken away, showing 
underneath the inner surface of the scutum, upper latus, 
tergum, and carinal latus. In other specimens figured by 
Fritsch (1887) and H. Woodward (1908) slight displacement 
of the valves has shown the inner surface of an underlying 
scutum. It is therefore certain that the whole of the 
capitular valves were paired, for, in addition to the lateral 
valves, the valves homologous with the carina can be shown 
to be paired, not only in S. pulchellum, but in S. haworthi. 
The split carina is very clearly shown in the specimen de- 
scribed as S. macadami, for fortunately a slight displacement 
of the upper plate shows part of the inner surface of the 
opposing plate along its entire outer margin: it is a pity that 
