260
J. A. KITCHING AND F. J. EBLING
As on the open coast, the relative radula length of P. vulgata within
Lough Ine decreases with decreasing level. The values of the radula
ratio for P. mpera are very low, although a comparison between Lough
Ine and Carrigathorna is complicated by a difference in range of shell
length; the means for samples taken within Lough Ine run from 0.82
to 0.90. It remains to be seen whether this is related to longer periods of
feeding associated with permanent immersion.
(c) Foot colour. Foot colour appears to have two components, dark pigment which is species-characteristic, and orange pigment which appears
to be environmentally acquired in relation to locality and level. P. vulgata has more dark pigment than P. aspera; thus in rock pools at
Carrigathorna, where neither species has orange pigment, the foot of
P. vulgata is dark grey and that of P. aspera white or pale grey. On open
rock a t Carrigathorna P. vulgata has a foot of ochre or of a mixture of
grey and orange; orange tends to increase towards the bottom of
its zone.
The foot of P. aspera has less grey colour. Towards the bottom of the
zone a t Carrigathorna it becomes a clear orange; within Lough Ine and
the Rapids it ranges from cream to apricot. We suspect a connection
with food.
(d) Shell form. The relative height of the shell is almost entirely related
to level. The lower it is on the shore the more depressed is the shell,
but there are no significant differences between the species at any
one level.
Within Lough Ine, sublittoral P. aspera has an extremely depressed
and crenulated shell, as though a continuous state of relaxation allows
the mantle margin to extend until it becomes wavy. On the Sill the
shell is relatively taller, but is nevertheless substantially more flattened
than on the open coast. It seems probable, therefore, that while exposure to air is the main environmental feature affecting tallness of the
shell, exposure to wave-action and current also have some effect.
c. SUBLITTORAL DISTRIBUTION I N THE LOUGH
We are at present only a t an early stage in the investigation of
changes in the fauna and flora with increasing depth in the lough. The
problem concerns not only the macroscopic benthos but also microscopic organisms such as diatoms on the surface of the mud and bacteria
upon and within it. We cannot yet discuss the vertical distribution of
algae in relation to illumination.
The outstanding characteristic of the lough is the discontinuity - in
summer - of temperature and of various chemical conditions at around
25 m. We have laid crab traps a t a range of depths leading down into
J. A. KITCHING AND F. J. EBLING
As on the open coast, the relative radula length of P. vulgata within
Lough Ine decreases with decreasing level. The values of the radula
ratio for P. mpera are very low, although a comparison between Lough
Ine and Carrigathorna is complicated by a difference in range of shell
length; the means for samples taken within Lough Ine run from 0.82
to 0.90. It remains to be seen whether this is related to longer periods of
feeding associated with permanent immersion.
(c) Foot colour. Foot colour appears to have two components, dark pigment which is species-characteristic, and orange pigment which appears
to be environmentally acquired in relation to locality and level. P. vulgata has more dark pigment than P. aspera; thus in rock pools at
Carrigathorna, where neither species has orange pigment, the foot of
P. vulgata is dark grey and that of P. aspera white or pale grey. On open
rock a t Carrigathorna P. vulgata has a foot of ochre or of a mixture of
grey and orange; orange tends to increase towards the bottom of
its zone.
The foot of P. aspera has less grey colour. Towards the bottom of the
zone a t Carrigathorna it becomes a clear orange; within Lough Ine and
the Rapids it ranges from cream to apricot. We suspect a connection
with food.
(d) Shell form. The relative height of the shell is almost entirely related
to level. The lower it is on the shore the more depressed is the shell,
but there are no significant differences between the species at any
one level.
Within Lough Ine, sublittoral P. aspera has an extremely depressed
and crenulated shell, as though a continuous state of relaxation allows
the mantle margin to extend until it becomes wavy. On the Sill the
shell is relatively taller, but is nevertheless substantially more flattened
than on the open coast. It seems probable, therefore, that while exposure to air is the main environmental feature affecting tallness of the
shell, exposure to wave-action and current also have some effect.
c. SUBLITTORAL DISTRIBUTION I N THE LOUGH
We are at present only a t an early stage in the investigation of
changes in the fauna and flora with increasing depth in the lough. The
problem concerns not only the macroscopic benthos but also microscopic organisms such as diatoms on the surface of the mud and bacteria
upon and within it. We cannot yet discuss the vertical distribution of
algae in relation to illumination.
The outstanding characteristic of the lough is the discontinuity - in
summer - of temperature and of various chemical conditions at around
25 m. We have laid crab traps a t a range of depths leading down into