172 PHOLADID A. 
I now come to the most decided difference between the 
two animals; the foot, in the form we are now describing, 
is proportionally larger than in any other of the Pholades, 
of hyaline texture, springing from the centre of the body 
with a long cylindrical pedicle; it has a subclavate appear- 
ance, truncate at the terminus, which is of suboval form and 
pointed anteally and posteally, and there is no outward visible 
trace of the curious elastic stylet common to all bivalves, and 
sO conspicuous in the ventral tissue of the form Pholadidea 
papyracea. 
I will now make a short comparison of the two forms: it 
will be observed that it is stated, in the form Pholadidea 
papyracea, that the mantle is closed, except a very small 
aperture or “spiracle” for the foot, if it still exists; but in 
the form Pholas lamellata there is a large aperture for a foot, 
that is, larger im proportion than in any of the Pholades. 
The branchiz, palpi, and elaborate siphonal apparatus are 
precisely the same, with only variations of colour; the bodies 
of the two are of the same shape, but differ in colour and 
markings, the one being intensely mottled, the other hyaline ; 
the body of the one having no foot attached to it, but the 
other a very large one. These are the principal variations, 
and certaimly constitute a very general difference of aspect 
between the animals of the two forms, and it must be admitted 
that conchologists and even malacologists, who have not 
examined with care all the conditions and incidents attached 
to them, have had a prima facie case for doubting their 
identity ; but notwithstanding these great and visible discre- 
pancies, I think I shall make out a case of identity. 
In the course of my examinations I was startled by the 
great variations in the organs of the two forms of this Pholas, 
which, twenty years ago, when I first examined this species, 
appear not to have so rigorously excited my notice; doubts 
arose in my mind, that I might be wrong in my former 
determinations of identity, and I wrote to Dr. Battersby to 
express them to him and Mrs. Griffith, both of Torquay ; the 
latter a lady naturalist, who has taken great interest im this 
question ; but in the summer of 1849, after a continued in- 
