EXPLANATION OF PLATE L 



Fig. I. — External structure of left valve of Rotundaria tnherculata 

 Rafinesque, 9 (Nat. size). 



Anterior end. 

 — Posterior end. 

 — Ventral side. 

 — Dorsal side. 

 — Antero-ventral side. 

 — Antero-dorsal side. 

 — Post-dorsal section. 

 — Post-ventral section. 

 — Nodule. 



ID. — Tubercle. — Umbonal region. 



1 1 . — Center of disk. 



I 2. — Lunule. 



13. — Beak, or umbone. 



14. — Ala, or dorsal ridge. 



15. — Costae. — Dorsal slope. 



16. — Post-umbonal ridge. 



17. — Rest lines of growth. 



18. — Minor lines of growth. 



Fig. 2. — Internal structure of right vavel of R. tuberciilata (Raf.) 9 

 (Nat. size.) 

 I. — Epidermis. 9. — Branchial cavity. 



— Outer nacreous zone. 



— Middle nacreous zone. 



— Inner nacreous zone. 



— Vein marks. 



— Retractor muscle scar. 



— Post, add. mus. scar. 



— Anterior adductor muscle scar. 



Lunular hinge. 

 Cardinal tooth. 

 Hinge tooth. 

 13. — Interdentum. 

 14. — Hinge ligament. 

 15. — Beak cavitiy. 

 16. ■ — Ala, or wing. 

 17. — Beak showing sculpture. 

 Fig. 3a. — Lateral view of juvenile R. tubercnlata showing sculpturing 

 of beak extending out on disk. (Nat. size). 



Fig. 3b. — Dorsal view of juvenile R. tuberculata showing beak sculpture. 

 (Nat. size.) 



Fig. 4. — Right side of close4 glochidium (X87) of R. tuberculata 

 {nov. glochidium) showing; — 



I. — Anterior end. 5. — Center of disk. 



2. — Posterior end. 6. — Adductor muscle. 



3. — Dorsal, or hinge line. 7. — Posterior adductor. 



4. — Ventral margin. 8. — Pericardial area. 



