76 NATURAL HISTORY. [UPPER FLOOR. 
which are peculiar for the foot being small, and fur- 
nished with a tuft of fibres at its base in front, by which 
the animal fixes itself to rocks, &c. This beard, as it is 
called in the last genus, issues out of a groove in the front 
of the right valve. The Pinnae, like the Pond Muscles, 
differ according to the place they inhabit. Those which 
live in smooth water are thin and covered with rows of 
small scales, while those that are found in rough water are 
thick and rugose. 
Then follow the genera Area , Peciunculus and Nucula , 
the animals of which have a large foot divided at the end, 
and the hinge formed of many interlocking teeth. In Area 
the end of the foot forms a glutinous secretion, which at 
length hardens, by which the animals attach themselves to 
rocks, &c.; and the shell is rhombic. In Peciunculus , the 
shell is orbicular, and the hinge line curved, while in Nucula , 
the hinge line is angular, with the cartilage placed in a 
pit at the angle. 
Lastly are placed the shells of the Branchiopc-dous Mol- 
lusca, which have tw r o ciliated arms, one placed on each 
side of the mouth. Of these, of which only two genera are 
found in Britain, viz. Terebratula and Criopus , the first is 
affixed by a tendon passing out through a hole in the upper 
valve, and the other is attached by the outer surface of its 
under valve. 
THIRTEENTH ROOM. 
The upright glazed Cases round the room contain 
the general collection of Birds. 
Cases 1 to 12 contain the Raptorial or Birds of Prey^ 
the Aecipitres of Linnseus, which constitute the first Order. 
They are characterized by strong feet with sharp claws, 
and a powerful bill, the latter covered at the base by a 
naked skin, or cere ; their stomach is almost entirely mem¬ 
branous, and sternum broad, giving attachment to the 
muscles of their long wings. Some of them feed chiefly 
by day; their eyes are placed on the side of their head, 
and the nostrils exposed, as in the family of Condors , 
(Cases 1 and 2,) found principally in America, which 
have naked heads and longitudinal nostrils : as the Condor, 
or Great Vulture of the Andes ; the Californian Vulture, 
