BIVALVES——OSTREA. 59 
These shells were formerly worn by pilgrims, on their 
hat or coat, asa mark of their having crossed the sea, 
for the purpose of paying their devotions at the holy 
shrine in Palestine: in commemoration of which they 
are still preserved in the armorial bearings of many fa- 
milies of distinction, whose ancestors had performed 
that ceremony. 
The third and remaining divisions of Ostreze consist 
of those which in construction, substance, and coloring, 
are more nearly allied to the common or eatable Oyster. 
The species are generally of a more irregular form than 
the Scallops. They are rough and plaited on the ex- 
terior, but the interior is smooth and glossy, and some of 
them have a steel-blue color or metallic lustre diffused 
over the surface. The most remarkable species of the 
third division is the O. malleus; in form it resembles a 
pick-axe: there are two varieties of it, viz. the white and 
the black, both of which, when in fine preservation, are 
highly esteemed, but the white variety is much more 
rare and valuable. Some species have the appearance 
of a dried leaf, as the O. folium and others of the fourth 
division; these are parasitical, and often attach them- 
selves to the roots and stumps of trees. 
The hinge of a few of the species, as the O. perna and 
O. isognomon, has a perpendicular grooved line. Some, 
as the O. vulsella, &c. gape at the hinge; others termi- 
nate in a long beak from the hinge upwards, as the O. 
cornucopie and O. virginica. 
The shells composing the third family of the fourth 
division, have been removed from the genus Mytilus to 
that of the Ostrea, to which they bear a much stronger 
resemblance. 
