BIVALVES — OSTREA. 59 



These shells were formerly worn by pilgrims, on their 

 hat or coat, as a 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 Ostreae 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 ti*ees. 



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. 

 cornucopisB 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. 



