BRACHIOPODA. 



and healthy condition of the animal, remains, we 

 believe, still to be proved by actual observation of 

 its manners. 



One side of each arm is fringed with a vast 

 number of long filaments, which are probably cili- 

 ated. In some fossil species, as the Spiriferadce, 

 the arms were permeated by an internal spire of 

 shell, of very numerous whorls ; while in some 

 recent species, they are supported by a shelly pro- 

 cess, which, springing from each side of the dorsal 

 valve, proceeds towards the margin of the shell, 

 then bending upward towards the opposite valve, 

 turns back upon itself, and forms a loop in the 

 centre of the cavity. This loop, being elastic, is 

 supposed to aid in the opening of the valves ; for, 

 being slightly compressed when they are closed, 

 they exert a pressure against the roof of the ven- 

 tral valve, and thus supply the place, in some 

 degree, of the tough and elastic ligament of the 

 CONCHIFERA, which is here entirely wanting. 



It appears, however, that the opening and clos 

 ing of the valves are more effectively provided for, 

 in the action of certain proper muscles, which are 

 antagonistic to each other. Four pairs of muscles 

 are inserted into the hollow of the ventral valve, 

 two pairs of which go across to the other valve, 

 and are inserted in front of the line which unites 

 the hinge-teeth. These answer to the adductor 

 muscles of the CONCHIFERA, as their contraction 

 draws the valves towards each other. Two other 

 pairs pass to that part of the dorsal valve which 

 lies behind the hinge-line ; and these by their con- 

 traction separate the margin of the valves. 



The BRACHIOPODA are never free, but invariably 

 attached to other bodies, occasionally, as in Crania, 



