THE BRACHIOPODS. S1é 
is found in the Indian Ocean and the Pacific as far as the 
coral zone extends. The animal 
of the tridacna, and of the near- 
ly related Hippopus, distinguishes 
itself by the beauty of its colours. 
The mantle of the Tridacna sa- 
franea, for instance, has a dark 
blue edge with emerald-green 
spots, gradually passing into a 
light violet. When a large num- 
ber of these beautiful creatures 
expand the velvet brilliancy of Hippopus maculatus. 
their costly robes in the transparent waters, no flower-bed on 
earth can equal them in splendour. 
Like the Lamellibranchiate Acephala, the Brachiopods are 
covered with a bivalve shell, but their internal organisation is 
very different. Instead of being disposed in separate gills, 
their respir. tory system is combined with the ciliated mantle on 
which the vascular ramifications are distributed, but their most 
striking feature is the possession of spiral fringed arms or 
buccal appendages which serve to open the shell and occupy 
the greater part of its cavity. These curious organs are in some 
Brachiopods quite free, in others attached to a complicated 
cartilaginous or calcareous skeleton. None of the existing 
molluscs of this class are capable of changing place, but are 
either fixed to extraneous substances by the agglutination of one 
of their valves or by a muscular peduncle passing through a 
perforation of their shells. There are no more than forty-nine 
living species, chiefly belonging to the genera Terebratula and 
Crania, and generally found at great depths in the Southern 
Ocean; but the fossil remains of 1,370 species prove their 
importance in the primitive seas, where they rivalled the 
lamellibranchiates in numbers and variety. Though now so 
rare or so local in the British seas that ordinary collectors are 
not likely to meet with any, they abound in many of our oldest 
rocks. A visit to the quarries at Dudley,” says E. Forbes, 
or an Irish lime-kiln, or an oolitic section on the Dorsetshire 
coast, or a green sand ravine in the Isle of Wight, will afford 
