3U 



PALEOZOIC SYSTEM OF ROCKS. 



General Description of a Brachiopod.— A Brachi- 

 opod shell consists of two valves, a dorsal and a ven- 

 tral. The ventral is the larger, and usually projects 

 beyond the dorsal, at the hinge, as a prominent beak. 

 This projecting portion is often perforated to give 



Fig. 339.— Rhynchone 



sulcata: side view, dorsal view, and showing 

 suture. 



n 



passage to a muscular peduncle, by which the shell is 

 attached in the living animal. The following figures 

 (Figs. 338-347) of Brachiopods, living and extinct, 

 will make these points clear. 



The viscera of a Brachiopod fill but a small space 

 in the shell, this 

 cavity being occu- 

 pied principally 



by two long spiral arms (hence the 



name), which probably subserve the 



Fig. 338. — Lingula 

 anatina, showing 

 the muscular ped- 

 uncle by which the 

 shell is attached. 



Fig. 340. 



Fig. 342. 



Figs. 340-342.— Showing toe Structure of Brachiopods: 340. Spirifer striates (Carboniferous): 

 a, dorsal surface; b, interior, showing the bony spirals. 341. Terebratula flavescens (living 

 species): a, exterior surface; b. showing bony structure for attachment of spiral arms. 342, 

 Spirifer hysterica (Carboniferous): a, exterior; b, showing bony spires. 



