MOLLUSCA. 187 
and connection of the valves. The cloak is likewise in the 
form of two leaves, corresponding with the valves which 
protect it. 
OrpER I.—BRACHIOPODA. 
Mouth with a spiral arm on each side fringed with fila- 
ments. 
The genera included in this group constitute the Bra- 
chiopoda of Cuvier. The lobes of the cloak are free an- 
teriorly. From the body, between the lobes, the arms have 
their origin at the margin of the mouth. These arms are 
capable of folding up spirally. All the species are perma- 
nently attached to foreign bodies, and inhabit the sea. 
Their nervous and reproductive systems have received but 
little elucidation. 
Ist Subdivision. 
Shell supported on a fleshy peduncle. 
Genus Linauta. Valves equal, the apex of both at- 
tached to the peduncle. 
The peduncle is nearly cylindrical, cartilaginous, and 
covered with a membrane consisting of circular fibres. The 
valves are oval, flat, and destitute of teeth, or elastic liga- 
ments. The adductor muscles are numerous, obliquely 
placed, and appear capable of giving to the valves a con- 
siderable degree of lateral motion. The cloak is thin, and 
has interspersed muscular fibres. Its margin is thickened, 
and fringed with fine hairs of nearly equal length. The 
arms are fleshy in their substance, conical, elongated and 
compressed in their form, and ornamented on the external 
surface with thick set fringes or tentacula. The mouth is 
