MOLLUSCOIDEA — BRACHIOPODS 



20I 



1. Sketch (a) side view of entire shell, (b) view looking fully 

 upon hinge line. Label in each the valves, cardinal areas, plica- 

 tions. 



2. Describe as much of the evolution of Platystrophia, noted 

 above, as is preserved upon the specimens at hand. 



What can you say as to its probable ancestry ? 





4. What is the significance of the name ? 



Fig. 83. — Rhynchotrema capax (Conrad), from the Upper Ordovician of Indiana. 

 Natural size. A, side view of the joined valve; b., brachial valve; p., pedicle 

 valve. B, brachial valve with beak of pedicle valve showing above. C, pedicle 

 valve showing the deep median depression. (From Indiana Survey.) 



Rhynchotrema (Fig. '^t,). Ordovician. 



Valves thick, very convex. Pedicle valve strongly incurved 

 at umbo, with thick concave deltidial plates. Entire surface 

 covered with strong, radiating plications crossed by many con- 

 centric growth lines. (Name from Greek rhynchos, a beak, + 

 trema, a hole ; the forms usually have the beak of the pedicle 

 valve perforated by a pedicle opening.) 



R. capax was widely distributed throughout the shallow 

 ocean covering much of North America during Upper Ordovician 

 time. In some adults a large pedicle opening is present, in 

 others it is absent. 



1. Sketch (a) side view of entire shell, (b) anterior view, (c) cut 

 portion of a vertical section through entire shell from beaks 

 forward. Label valves, plications, growth lines, mnbos. 



2. Was this specimen attached or free when adult ? Reasons. 



3. By means of an ideal sketch, explain how the shell was 

 built ; what do the growth lines represent ? 



