EXPLANATION OF PLATE XXI. 



Figs. 1-4. RHIPIDOMELLA OWENI Hall & Clarke. p. 151 



1-2. External and internal views of a nearly perfect pedicle valve. 

 (W. M., No. 4675.) 3-4. External and internal views of a 

 nearly complete brachial valve. (W. M., No. 7857.) 



New Providence shale, Button Mould Knob, Kentucky. 



Figs. 5-7. RHIPIDOMELLA BURLINGTONENSIS (Hall) p. 149 



5. View of a nearly perfect pedicle valve. (W. M., No. 11893.) 



Burlington limestone, Sagctown, Illinois. 



6. Similar view of another pedicle valve. (W. M., No. 7858.) 



Burlington limestone, Burlington, Iowa. 



7. Pedicle view of an internal cast, a little restored at the beak. 



(W. M., No. 13045.) 



Chert of Burlington limestone, Pike County, Missouri. 



Figs. 8-27. RHIPIDOMELLA THIEMEI (White) p. 155 



9-18. External and internal views of five pedicle valves. 19-24. 

 External and internal views of three brachial valves. 25-27. 

 Pedicle, brachial and lateral views of a nearly complete speci- 

 men. Cotypes. (U. M., No. 1348.) 



Kinderhook, Bed No. 7, Burlington, Iowa. 



8. View of a nearly perfect pedicle valve. (W. M., No. 6670.) 



Kinderhook, Bed No. 6, Burlington, Iowa. 



Figs. 28-32. SCHIZOPHORIA SEDALIENSIS n. sp p. 164 



28-31. Pedicle, brachial, lateral and posterior views of a nearly 

 perfect specimen. 32. View of the interior of an incomplete 

 pedicle valve, showing the muscular scar. (W. M., No. 14225.) 

 Upper Chouteau limestone, Sedalia, Missouri. 



Figs. 33-34. SCHIZOPHORIA sp. 



33. View of the internal cast of a brachial valve. 34. View of an 

 incomplete internal cast of a pedicle valve. (U. Ml, No. 1351.) 

 Chonopectus sandstone, Burlington, Iowa. 



48 



