MOLLUSCOIDEA — BRACHIOPODS 



201 



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. 



3. 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. 83). 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, 4- 

 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, umbos. 



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 ? 



