86 Palaeontographica Americana 86 



PlyATE IX 



Figure Page 



1. Area santarosana Dall 38 



Oligocene of Oak Grove, Florida. The posterior ribs are obscured by the illu- 

 mination. 



2. Interior of the same. 



3. Area santarosana Dall; Oligocene of Oak Grove, Florida; right valve. 



4. Area staviinata Dall 39 



Probably from Alum Bluff; the upper part of the posterior margin is slightly 

 broken. 



5. Area staniinata Dall; Oligocene of the lower bed at Alum Blufif, Florida; interior of 

 a right valve. 



6. Area staminata Dall; Oligocene of Bailey's Ferry, Florida; exterior of a young 

 right valve. 



7. Area staniinea Say 39 



Miocene of Choptank River, Maryland; an unusual form, figured to show the 

 variation of this species. 



8. Area staminea Say; Miocene of Choptank River, Maryland; valve with grooved 

 ribs. 



9. Area stamitiea Say; Miocene of Choptank River, Maryland; common form. 



10. Interior of the same. 



11. Area slafninea Say; Miocene of Governor's Run, Maryland; short, high form. 



12. Interior of the same. 



13. Area stami?iea Say; Miocene of Choptank River, Maryland; short, high form. The 

 umbo is angular and pointed instead of roundly inflated like the preceding. 



14. Area idonea Conrad 41 



Miocene of St. Mary's River, Maryland. This is the form abundant at St. 

 Mary's River. 



15. Interior of the same. 



16. Area idonea ConvaA; Miocene of the upper bed at Alum Bluff, Florida. This is 

 not very close to A. idonea from Maryland. 



.17. Area idonea Conrad; Miocene of the upper bed at Alum Bluff, Florida; an extreme 

 variation. 



