Pvn H,i I'UitlS

MYTILUS. 113
dermis of immature shells is yellowish-brown, and has
an agglutinating property, being frequently coated with
gravel and bits of shell. In this state the dorsal angle
is more acute. Rude nests or cases are occasionally
made by the young for their protection. The spots
where pearls are in course of formation exactly corre-
spond with the holes drilled by species
of the curious
called Cliona from the outside of the shell. A
sponge
transverse section admirably displays the mode of growth
and secretion of colour. The outside layers are purple ;
while the inner layers, which are three times as thick
and numerous as the others in full-grown shells, are
white. The "horse-mussel/' as it is called,
enormous size under favourable circumstances. One of
my specimens, which Professor King got
attains an
on the Nor-
thumberland coast, is about nine inches and a quarter
long and of a proportionate breadth and capacity. It
would have made a dainty drinking-cup for Mimer, or a
pretty toy for one of the other giants,
'
slager sung in his Nordische Guder/
of whom Ohlen-
"And all round the cavern might plainly be seen,
Where Giants had once been at play ;
For the ground was with heaps of huge muscle-shells strewn,
And strange fish were mark'd in the clay."
This is the Modiola papuana of Lamarck, but not the
Mytilus Papuanus of D'Argenville, which is a tropical
species. The former referred to his Modiola tulipa the
Mytilus modiolus of Linne. Mr. Hanley also states that,
from an examination of the typical specimens, the M.
modiolus of Linne is not our species but the Modiola
tulipa of Lamarck. This shows the discrepancy between
the Linnean collection of shells and the '
System a Naturae/
and how little reliance can now be placed on the
former for identifying some of the species. Linnets de-