CLASS BRACHIOPODA. 131 
THE FIFTH CLASS OF THE MOLLUSCA. 
BRACHIOPODA. 
THE mollusca brachiopoda, like the acephala, have a 
bilobed mantle, which is always open. Instead of feet, they 
are provided with two fleshy arms, furnished with numerous 
filaments, which they can protrude from and draw into the 
shell. The mouth is between the base of the arms. Neither 
their organs of generation, nor their nervous system, are well 
known. 
All the brachiopoda are provided with bivalve shells, fixed 
andimmovable. But three genera are known. 
LINGULA, Brug. 
Two equal, flat, oblong valves, the summits of which are at 
the extremity of one of the narrow sides, gaping at the other 
end, and attached between the two summits to a fleshy pedi- 
cle, which suspends them to the rocks; the arms become 
spirally convoluted previously to entering the shell. It ap- 
pears that the gills consist of small leaflets, disposed around 
the internal face of each lobe of the mantle. 
But a single species, Lingula anatina, Cuv. Ann. du Mus. 
I. vi.; Seb. II. xvi. 4, is known. It inhabits the Indian 
Ocean, and has thin, horny, and greenish valves. 
TEREBRATULA, Brug. 
Two unequal valves, united by a hinge ; the summit of one, 
more salient than the other, is perforated to permit the passage 
K 2 
