EXPLANATION OF PLATE XX. 



Figs. 1-8. RHIPIDOMELLA MISSOURIENSIS (Swallow) p. 148 



1-3. Pedicle, brachial and lateral views of a very perfect specimen. 

 4-6. Similar views of another specimen. 7. Internal view of a 

 pedicle valve, showing the muscular scar. 8. Internal view 

 of a brachial valve. (W. M., No. 6692.) 

 Louisiana limestone, Louisiana, Missouri. 



Figs. 9-18, 30-35. RHIPIDOMELLA DIMINUTIVA Rowley p. 153 



9-11. Pedicle, brachial and lateral views of a nearly complete 

 specimen. (R. R. R.) 12-13. Pedicle and brachial views of 

 another example. 14. Internal view of a pedicle valve. 15. 

 Internal view of a brachial valve. (W. M., No. 14222.) 



Burlington white chert, Louisiana, Missouri. 



16-18. Pedicle, brachial and lateral views of a nearly complete 

 specimen. (W. M., No. 8552.) 



Pier son limestone, near Springfield, Missouri. 



30-32. Pedicle, brachial and lateral views of a very perfect speci- 

 men, similar in size to the type specimen. 33-35. Views of the 

 same specimen enlarged (x2). (R. R. R.) 



Burlington white chert, Louisiana, Missouri. 



Figs. 19-21. RHIPIDOMELLA sp. 



Brachial, lateral and pedicle views of a nearly complete but 

 slightly distorted specimen. (W. M., No. 14220.) 



Fern Glen formation, near Kimmswick, Missouri. 



Figs. 22-26. RHIPIDOMELLA DUBIA (Hall) *. . .p. 160 



22-24. Pedicle, brachial and lateral views of a very perfect ex- 

 ample. 25-26. Internal views of two pedicle valves. (W. M., 

 No. 13055.) 



Salcin limestone, Spcrgen Hill, Indiana. 



Figs. 27-29. RHIPIDOMELLA TENUICOSTATA n. sp p. 158 



27. Pedicle view of a nearly complete specimen. 28. Brachial 

 view of another specimen. 29. Interior view of a brachial 

 valve. Cotypes. (W. M., No. 9673.) 



Chouteau limestone, Pettis County, Missouri. 



Figs. 36-43. RHIPIDOMELLA JERSEYENSIS n. sp .p. 157 



36-38. Pedicle, brachial and lateral views of a nearly complete 

 specimen. 39. View of a brachial valve. (W. M., No. 7843.) 



Fern Glen formation, near Elsah, Illinois. 



40. Internal view of a pedicle valve. (W. M., No. 4691.) 41. In- 

 ternal view of another pedicle valve. 42-43. Internal views of 

 two brachial valves. (W. M., No. 4692.) 



Fern Glen formation, near Kinnnswick, Missouri. 



46 



