THE MOLLUSCA OF THE ISLE OF MAN. 881 
one must be attributed to some such incident as the imbedding of 
the living mollusk in the tangled roots of some Fucus clinging to 
the oysters or cirrhipedes so wont to congregate upon ship timber 
in a foreign port, and the subsequent detachment of the seaweed 
either in the process of careening, or perchance by the breaking 
up of the vessel itself.’ As I believe no other observer since 
Forbes wrote has found another specimen on our British coasts, I 
presume that this specimen must be considered as a waif from a 
foreign shore. 
On two undoubted species of our Mollusca I would make a few 
remarks before closing this paper. One is Unio margaritifera. 
Forbes writes, in the ‘Malacologia Monensis,’ “In the Black 
River; common near Braddan Church. It was formerly much 
sought after by the inhabitants for the sake of the pearls which it 
not unfrequently contains.” In the ‘ British Mollusca’ we read, 
“ The variety Royssii of this Unio was formerly much sought for 
in the river near Braddan, in the Isle of Man, on account of its 
pearl,” and, on the following page, “ The streams of the Isle of 
Man.” Mr. Garner, in his ‘ Holiday Excursions of a Naturalist,’ 
p. 72, on mentioning Kirk Braddan, says:—‘‘ We searched the 
little river for a mile or more, for a variety of the pearl-mussel, 
Alasmodon Royssii, mentioned by Mr. Forbes as found here. I 
only satisfied myself that it existed by picking up a fragment of a 
valve.” Is this once much-prized bivalve extinct in Man, or fast 
becoming so? I once, some years ago, searched long in vain for a 
specimen, and I have not heard of anyone since Professor Forbes 
finding this bivalve. The other species to which I have alluded 
is the Orbicula norvegica of the ‘ Malacologia Monensis,’ and the 
Crania anomala of the ‘ British Mollusca.’ In the latter work it 
is called a “ curious bivalve,” as indeed it is, and is stated to have 
been ‘“‘added to the British list by Dr. Fleming, who found it 
adhering to stones, from deep water in Zetland; since then 
it has been taken abundantly in several localities, chiefly on the 
west coast of Scotland.” In the ‘ Malacologia Monensis’ Forbes 
says, “ A single specimen dredged at Ballaugh, Oct., 1834.” The 
peculiar interest that attaches to this mollusk is owing to the 
circumstance that it belongs to a family and class which held 
a much more important position anciently in the population of the 
seas than it holds now. It is one of the five existing species of 
the Craniide, of which thirty-seven species are known in the 
