223 
over the carina has its umbo at or near the apex; in some Scal- 
pellum -species the umbo is through growth secondarily removed 
somewhat down the plate, although never reaching the middle of 
the plate. In the scuta the umbo is invariably situated at the 
apex. 
The family has evidently been limited in the same way by 
Pilsbry (1916, p. 14), and there is no reason to change the 
name Scalpellidae given by him already in 1907; nor is the gap 
between Ibla and the other genera large enough to defend the 
proceeding of Annandale (1909) who places this genus in a 
family of its own. 
The other pedunculated cirripeds show quite different lines of 
development. The first difficulty arising here, is the question, 
which genus is the most primitive. Taking again into consideration 
that the ancestral form of the recent cirripeds has after all had 
a skeleton of five primordial valves, we can at once discard a 
theory of the genera with reduced number of plates as primitive. 
We shall, therefore, have to chose between the genera with five 
plates i. e. Oxynaspis, Lepas, Poecilasma, Megalasma, and Octolas- 
mis. As to the last named genus we can at once leave it out of 
the discussion; the species give clear evidence of the reduction 
by a splitting up of the plates being due to adaptation : the more 
specialised the biology (as f. inst. the life in the gili chamber of a 
crab) the farther the reduction has proceeded; also the special bio¬ 
logy of more of the species designates it as a more specialized 
genus. The same applies to Oxynaspis , although this genus by many 
authors has been considered a very primitive one; its peculiar com- 
mensalism with Anthipatharians, which has resulted in the latter 
enveloping the cirriped in its tissues, decidedly evince the well 
adapted, i. e. from the parent stock probably more or less differ¬ 
ent genus. 
In Megalasma the individual development clearly tells us that 
the position of the scutal umbo at the occludent margin above the 
basal angle of the plate is a secondary feature, and that the pre- 
decessors of the genus have had basal umbo of their scuta. Thus 
only two genera are left, viz. Lepas and Poecilasma, and here we 
are at a loss. With our present knowledge it is impossible to say 
