570 



Class BRACHIOPODA. 



Animal furnished with a pair of cirrhated arms or oral 

 appendages, which are free or united by membrane, some- 

 times supported by calcareous processes. Mantle-lobes 

 closely applied to the valves, fringed with horny seta, and 

 supplied with branching veins ; gills none, respiration per- 

 formed by the vessels of the mantle. Foot none. 



Shell inequivalve, attached to submarine bodies by a 

 muscular peduncle, or by the substance of its ventral valve ; 

 valves dorsal and ventral, united by muscles, and usually 

 articulated by teeth. 



Marine. 



In this Class of Molluscous animals the most curious 

 feature consists in the mouth being furnished with two 

 folded or spiral labial appendages or oral arms, united by 

 membrane, fringed with cirrhi, and supported by an internal 

 shelly skeleton. In some of the genera the ends of the 

 spiral arms are endowed with voluntary motion, the move- 

 ment being effected by the injection of a fluid into the 

 hollow spiral tube, by means of which the coils are sepa- 

 rated. The arms, however, cannot be protruded from the 

 shell, but are usually confined to one position by the mem- 

 brane which unites them. Their nervous system, like that 

 of other Mollusca, is composed of several medullary masses 

 which surround the gullet and send filaments to the various 

 organs of the body ; their organs of taste, if they indeed 



