225 
in Conchoderma leads on to Alepas; again the mouth feet, espec- 
ially the peculiar, terraced construction of the cutting edge of the 
maxilla and the many teeth of the mandible point to a doser re- 
lationship with the latter form than with any other genus of the 
group. Alepas has also kept the filamentary appendages. 
The other genera, on the other hånd, seem to have arisen from 
Poecilasma. The step from this genus to Megalasma is indeed so 
short that we may doubt the correctness of a separation; many of 
the species of the latter genus have been ranged with Poecilasma, 
till Pilsbry (1907) laid a new foundation for the generic separ¬ 
ation ; nevertheless, the question whether these genera were not 
more correctly to be merged into one can by no means be re- 
garded as settled. — In Megalasma the scuta tend to bring the 
basal margin in line with the occludent margin by a rotation round 
the umbo; this tendency is also seen in Oxynaspis, although not 
so distinctly. Moreover the carinal umbo in this latter genus is mov- 
ing upwards along the dorsal line, although never passing by the 
middle of the plate; in some Poecilasma — and Lepas — species a 
„basal plate“ is indicated in the carina below the umbo, and this 
has now in Oxynaspis attained a rather high development. The 
maxilla of Oxynaspis decidedly point to a nearer relationship with 
Poecilasma than with Lepas, and the habitat of the genus is also 
more in conformity with the deeper living species of Poecilasma. 
In Poecilasma as in Lepas some species show a tendency to- 
wards a reduction of the calcification, and towards a splitting up 
of the outer parts of the plates. This leads from Poecilasma into 
Octolasmis, in which genus the biological conditions favour a ske- 
letonal reduction. To this generic line — although probably not 
directly through Octolasmis — Heteralepas links itself. One might 
believe in a doser relationship between this genus and Concho¬ 
derma, when judging by the external appearance. But the mouth 
parts of Heteralepas, and especially of the subgenus Heteralepas 
s. str. are directly identical with those of Poecilasma and strikingly 
in contrast with those of Lepas, and Conchoderma. Owing to the 
great conservatism of these organs in the cirripeds we must ascribe 
a great phylogenetic value to them. 
According to this, we find in this family two fine examples of 
convergence represented by the lines of develbpment of Poecilasma 
Vidensk. Medd. fra Dansk naturh. Foren. Bd. 73. 
15 
