BRACHIOPODA. 



439 



are called the " lobes " of the " pallium/' or " mantle." The 

 digestive organs and muscles occupy a small space near the 

 beak of the shell, which is partitioned off by a membranous 

 septum, which is perforated by the aperture of the mouth. 

 The remainder of the cavity of the shell is almost filled by 

 two long oral processes, which are termed the " arms," and 

 from which the name of the class has been derived (fig. 278, 

 D). These organs are lateral prolongations of the margins 



D 



Fig. ytS.Terebratula (Waldheimia) flavescens. A, The shell viewed from behind, showing 

 the dorsal valve, and the perforated summit of the ventral valve above it ; B, Inner view of , 

 the dorsal valve, showing the shelly loop (I) which supports the spiral arms ; c, Inner view 

 of the ventral valve, showing the foramen or aperture (/) in the beak, through which the 

 muscular stalk of attachment passes ; D, Longitudinal and vertical section of th,e animal, 

 showing the spiral arms (a), the stomach (s), and the liver (h). At / is the opening in the 

 beak, with the stalk of attachment (p) passing through it. (After Davidson and Owen.) 

 Some details have been omitted in figs. B, c, and D, for the sake of clearness. 



of the mouth, usually of great length, closely coiled up, and 

 fringed on one side with lateral processes, or " cirri." In 

 many Brachiopods the arms are supported upon a more or 

 less complicated internal calcareous framework or skeleton, 

 which is sometimes called the " carriage-spring apparatus." 



In some forms, as in the Terebratulidce (fig. 278, B), the 

 internal skeleton which supports the arms is a short shelly 



