202 AN INTRODUCTION TO THE STUDY OF FOSSILS 



4. In sketch i (c) indicate by drawing in the muscles how the 

 valves were opened and closed. 



5. How do brachiopods eat? Breathe? 



6. Do brachiopods live in the sea or in fresh waters ? 



7. At what depths do they live? 



Terebratula-like forms (Fig. 84). Devonian to present. 



Shell usually biconvex, and elongate oval. Pedicle valve 



has generally a large circular pedicle opening (whence the 



name from the Latin diminutive 

 of terebratus, perforated). Deltid- 

 ial plates prominent. The old 

 genus Terebratula has been sub- 

 divided into many genera. 



Rensselaeria is an ancient type 

 from the lower Devonian of North 

 America and Europe. Terebratula 

 harlani is a large form abundant 

 in the Cretaceous of the Atlantic 

 coast of North America, where 

 also is the coarsely punctate 

 species Terebratella plicata. For 

 Terebratulina septentrionalis see 

 page 181. 

 Note the large pedicle opening, deltidial plates and micro- 

 scopic punctae of T. harlani, the coarse punctae of T. plicata. 



Atrypa (Fig. 85). Silurian to top of Devonian. 



Pedicle valve slightly convex, brachial usually very convex. 

 Entire surface radially plicate, crossed by many more or less 

 prominent concentric lamellae of growth. Apices of spiral bra- 

 chidia directed towards middle of brachial valve, hence the 

 strong convexity of this valve. 



Atrypa reticularis is very abundant throughout the world in 

 the Silurian and Devonian. The Silurian forms are usually 

 smaller with brachial valves much less convex and with less ex- 

 tensive lamellae than the Devonian forms. 



Fig. 84. — Terebratula harlani Mor- 

 ton from the Cretaceous of New 

 Jersey. A, brachial valve, with 

 pedicle opening (ped.o.) of oppo- 

 site valve showing above. B, 

 surface of pedicle valve. ( X 2-) 

 (After Whitfield.) 



