328 



POPULAR CONCHOLOGY. 



The Brachiopoda are divided by Gray into three orders : 

 — Ancylopoda, the animal having mouth arms, which 

 are not spirally rolled ; Helictopoda, having arms spirally 

 rolled, and supported by a spiral appendage within the 

 valves ; and Rudist<<e, the animal of which is not known. 



Order I. 



ANCYLOPODA. 



The mouth arms are curved backwards (not spirally 

 rolled), and attached to a solid shelly appendage in the 

 ventral valve ; they are only dilatable at the point, or not 

 at all; the mantle adheres firmly to each valve in con- 

 sequence of fine processes, which project into the pores 

 of the shell. The shell is delicate, and drilled, or punc- 

 tured throughout its whole substance ; the stage on which 

 the arms of the animal hang, springs either from the hinge 

 of the ventral valve, or is fastened to a lamellated middle 

 rib of the same; the dorsal valve is beaked, and has a 

 hole at the boss, whence a sinewy stalk proceeds, by 

 means of which the animal attaches itself to foreign sub- 

 stances. In some individuals this hole is obliterated in 

 age ; the hinge is furnished in each valve with two teeth, 

 of which those in the dorsal are separated, and clasp be- 

 tween them the two in the ventral valve ; these lock so 

 firmly into each other that they cannot be separated 

 without injury. 



