94 Palaeontographica Americana 94 



PI^ATB XIII 



Figure Page 



1. Area campsa Dall 54 



Miocene of the upper bed at Alum Bluff, Florida; old right valve. 



2. Interior of the same, showing the thickening of the anterior end of the hinge. 



3. Ana campsa Dall; Miocene of the upper bed at Alum Bluff, Florida; umbonal view 

 of an adult specimen, broken posteriorly. 



4. Area riistiea Tuomey and Holmes 55 



Pliocene of Shell Creek, Florida; exterior of a young left valve. 



5. Area rustiea Tuomey and Holmes; Pliocene of Shell Creek, Florida; interior of a 

 young left valve. 



6. Area catasarca Dall 56 



"Pliocene of Alligator Creek, Florida; S5 mm."; after Dall. 



7. Area initiator Dall 5^ 



Oligocene of Sour Lake, Texas; X2.7; interior of a large left valve. 



8. Umbonal view of the same. Near the center of the ligament area on this specimen 

 there is an incipient second v-shaped groove. It was lost in the engraving. 



9. Area initiator Da.]]; Oligocene of Sour Lake, Texas; X 2.7; exterior of a left valve. 



10. Area scalaris Conrad 57 



"Exterior of left valve, and hinge and teeth of right valve"; after Tuomey 

 and Holmes. 



11. Area sealaris Conrad; Miocene of North Carolina; exterior of a small right valve, 

 showing the interstitial ribs. 



12. Area sealarina 'R&Wprrn; Pliocene of Shell Creek, Florida; interior of a left valve 

 lent by the U. S. National Museum. The teeth are worn. This figure shows the 

 cardinal area characteristic of Cunearca. 



