378 On the Morphology of some Cretaceous Cirripedes. 
the valves, there is much resemblance to the forms of 
Scalpellum included in the subgenus Areoscalpellum. This 
is more especially marked in the case of the upper whorl 
of valves which agree almost exactly in disposition, and 
except for the more simple carina, which is not divided off 
into tectum, parietes, and intraparietes, there are no dis- 
tingwishing "features. While there is a somewhat similar 
disposition of the lower whorl of valves to that in Arcoscal- 
pellum there is a great difference structurally, for the 
inframedian latus overlaps the rostral and carinal latus on 
either side; the. lower lateral plates are hardly at all 
specialized, for the rostral and inframedian latus are almost 
exactly alike in shape and size, and resemble very much the 
carinal latus, which, however, is about twice as large as the 
rostral and inframedian Jatus ; the rostrum is comparatively 
very much greater in size than in any known Arcoscalpellid, 
in which latter it becomes exceedingly small or is entirely 
absent in the more recent forms. Crediscalpellum is clearly 
related to Arcoscalpellum, but, while the valves have com- 
bined to form a somewhat similar capitulum, the individual 
valves, especially the carina and the lower latera, still retain 
their primitive structure, and have not become so specialized 
in shape as in Arcoscalpellum and the more specialized forms 
of Scalpellum, s. str. 
There would seem to be some relationship also to Calaniica 
(Scillelepas), especially in the lower whorl of valves. In 
Scillelepas there is no upper latus interposed between the 
scutum and tergum, the valve which is homologous with 
the upper latus in other forms being still a member of the 
lower whorl. The valves of the lower whorl in Sez/elepas 
are not so differentiated in shape as in Arcoscalpellum, 
although more so than are the valves of Cretiscalpellum, and 
the median latus does not overlap the rostral and carinal 
latus, but on the contrary is overlapped on each side by 
those valves. 
The structural resemblance of Cretiscalpellum is therefore 
closest to Arcoscalpellum, and this probably mdicates not 
that <Arcoscalpellum was derived from Cretiscalpellum, but 
that they had a common ancestor, which in some way was 
related to Scillelepas. 
Arcoscalpellum has a known range from the Lower Cre- 
taceous (Aptian) to Recent, ‘refiscalpellum is known to 
exist still earlier in the Lower Cretaceous, for it oecurs in 
the Neocomian, but it is not known more recent than the 
Danian, and Scillelepas has a known range from the Upper 
Cretaceous (Upper Senoman) to Recent, although it is 
probable that 1t existed in the Jurassic rocks. 
