Cakditid^ MOLLUSCA. Ajsodokta. 
ton Channel and Behring’s Straits to the Egean Sea, 
and in depth from thirty to one hundred and twelve 
fathoms. 
Family— OARDITID^. 
Tlie species of this family have an ovate or cordate 
shell, with the surface marked externally with strong 
radiating ribs. The hinge Ls furnished with two oblique 
diverging cardinal teeth directed towards the same side, 
and no laterals ; the ligament is external. The species, 
which muster upwards of fifty in number, are usually 
obtained from deep water, on rocky bottoms in tropical 
seas, though some are found also in shallow water and 
on the shores of North America. 
In the genus Cardita the shell is oblong; while in 
Venericardia it is cordate and ventricose. 
Family — CRASSATELLIDiE. 
In this family the shell is solid, ventricose, attenuated 
posteriorly, smooth or concentrically furrowed, and of 
a porcellaneous texture. The hinge is furnished with 
two subdiverging, striated, cardinal teeth placed in 
front of a cartilage pit, and one lateral tooth in each 
valve. The ligament is internal, inserted in a pit in 
each valve. The species, which are about thirty in 
number, are usually dredged from deep water, and are 
chiefly found in the Australian seas, though some have 
also been obtained from India, Africa, and South 
America. None have as yet been discovered inhabit- 
ing Europe. 
Family— UN lONIDiE. 
The River Mussels secrete a byssus in the very young 
state. The shell is usually regular, equivalve, and 
closed. Externally it is covered with a hard, smooth, 
olivaceous epidermis, beneath which it is beautifully 
pearly. The ligament is external, large and promi- 
nent, and the hinge is variable. The River or Pond 
Mussels are found in fresh- water lakes, rivers, and 
ponds throughout the whole world. About three 
hundred species have been described — the greater num- 
ber being natives of North America. In Asia and 
South America a considerable number occur; and 
though only a few species inhabit Europe, the number 
of individuals belonging to them is very great. In the 
UmonidcB the sexes are distinct, and the eggs in the 
females are contained in the outer gills, which in 
winter and early spring are found to be full of them. 
The fry spins a delicate, ravelled byssus, and flaps 
its triangular valves with the i>osterior shell-muscle, 
which is largely developed, whilst the other is yet in- 
conspicuous.” — {Woodward.) At this season. Lister 
says that the Unio pictorum has the fetid smell of the 
goat. 
Genus Unio. — This genus contains about two hun- 
dred and fifty species, which, as may be supposed, 
differ considerably amongst themselves in shape and 
general appearance. The inside of the valves is gene- 
rally brilliantly nacreous, and the hinge is furnished 
with (often strong) cardinal teeth, and very elongated 
371 
laminar laterals. The U. piclorum or Painter’s Mus- 
sel is extensively used for containing gold and silver 
paint. 
Genus Damaris {=Margaritana'). — This genus 
only differs in the posterior or lateral teeth being nearly 
obsolete. The only species of this genus is the Pearl- 
mussel, Damaris inargaritifera. It is found in the 
rivers and mountain streams of Britain, Lapland, and 
North America. At the present day the animal is 
used by the fishermen in Scotland as a bait. Many 
boat-loads “ are taken from the mouth of the Ythen, a 
river not far from Aberdeen, and employed in the 
fisheries of cod and ling, established near Peterhead.” — 
{Johnston.) In former times, in the same country, these 
shell-fish were used as an article of food by the na- 
tives ; “ and such is their estimation among the deintiest 
kinds of food,” says Boetius, in his account of Scotland, 
“ that they were not unworthilie called, of old time, 
widowes’ lustes.” The pearls found in this shell are 
bright and of excellent lustre. At Perth there was an 
extensive fishery in the river Tay, which continued 
up to the end of last century, and which Pennant tells 
us had from 1761 to 1764 produced pearls worth 
£10,000. The fishery, however, we are also told, 
was exhausted by the avarice of the undertakers, and 
soon after ceased to be productive. In the river 
Conway, in North Wales, excellent pearls have been 
found ; and it is said that Sir Richard Wynn of Gwydir, 
chamberlain to Catherine, queen of Charles 11. , pre- 
sented her majesty with one taken from that river, 
which is to this day honoured with a place in the royal 
crown. In Ireland also a considerable fishery existed • 
as long ago as 1690. Sir Robert Reading informs us 
that he had seen a pearl, taken in the county Tyrone, 
that weighed thirty-six carats, and was valued at £40. 
He also says “ that a miller found a pearl which he 
sold for £4 10s. to a man that sold it for £10, who 
disposed of it to the Lady Glenawly for £30, with whom 
he saw it in a necklace, for which she refused £80 
from the old Duchess of Ormond.” 
Genus Barbala. — This genus has a single linear 
tooth under the dorsal margin, extending the whole 
length ; and the valves are produced at the back into a 
thin elastic dorsal wing. Barhala pHcata, perhaps the 
only species, is the famous Chinese Pearl Mussel. The 
people of the Celestial Empire produce artificial pearls 
in this shell, by introducing wire and other foreign 
bodies under the mantle of the animal. In the British 
Museum, specimens may be seen where pearls of a 
fine lustre have been thus produced, as well as a 
series of little “josses,” made of metal, and which, 
having been introduced under the mantle while the 
animal was alive, have gradually become quite coated 
with pearly matter. 
Genus Anodonta. — This genus has the hinge per- 
fectly toothless. The shell is generally thin, some- 
times of large size, oval, smooth, compressed when 
young, but becoming ventricose by age. The species 
number about fifty, the greater number of which are 
natives of the fresh waters of North and South Ame- 
rica. They are very prolific ; and Mr. I. Lea, who 
has paid great attention to the study of this family, has 
computed that the outer gills of a female has contained 
