448 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



Fig. 3. Brachial valve in which the differentiation between the fold and right slope 

 is lost. 



4. Pedicle valve of the same specimen. 



Richmond group (Arnheim formation), Brush Run, 1 mile east of Seatonville, 

 Kentucky. 



5. Brachial valve of a specimen in which the fold is asymmetrical. 



Richmond group (Arnheim formation), one-fourth mile east of Fisherville, 

 Kentuckj-. 

 Figs. 6-8. Platystrophia ponderosa arnheimensis, new variety, p. 428. 



6. Anterior view. The thick valves and coarse pliations are characteristic. 

 Richmond group (Arnheim formation), 1^- miles west of Clark, Kentucky. 



7. Pedicle valve of a mutation with four plications in the sinus. 



Richmond gi'oup (Arnheim formation), Brush Run, 1 mile east of Seatonville, 

 Kentucky. 



8. Brachial valve of a specimen with a short hinge. 



Richmond group (Arnheim formation), I^ong Run, three-fourths mile above 

 Boston, Kentucky. 



Plate 52. 



All figures on this plate are natural size. 

 Figs. 1-3. Platystrophia ponderosa, variety. 



1. Brachial valve of a mutation with five plications on the fold. 



2. Cardinal view, 



3. Pedicle valve. (Same specimen as fig. 1.) The illustration sho-^fs four pli- 



cations in the sinus. 

 This variety is characterized by its transverse form, 

 Richmond group (Arnheim formation), one-fourth mile east of Fifiherville, 



Kentucky, 

 Figs. 4-6. Platystrophia, species. 



4. Cardinal view. 



6. Pedicle valve. This variety has a broad shallow sinus and acuminate hinge 



extremes. 

 This form has many characters in common with those illustrated in plate 50, 



figs. 5, 8-11. 

 Richmond gi-oup (Arnheim formation), 1 mile east of Seatonville, Kentucky, 



on Floyd's Fork. 



5. Brachial valve showing the low rounded fold. 

 Richmond group, Lebanon, Ohio. 



Figs. 7. Platystrophia ponderosa Foerste. 



Interior view showing the deep muscle scars and the articulation. 



Maysville group (Bellevue member), Madison, Indiana. 

 Figs. 8-9. Platystrophia ponderosa, variety. 



8. Anterior view of a similar specimen. 



Richmond group (Arnheim formation), 1 mile east of Seatonville, Kentucky. 



9. Brachial valve of a mutation with seven plications on the fold, 

 Richmond group, 4 miles northeast of Gallatin, Tennessee. 



Fig. 10. Platystrophia ponderosa Foerste. 



10. Interior view of the brachial valve, c. cardinal area; cp. cardinal process; d, 



delthyrium; m. muscle scar; s. septum; t. teeth, 

 Maysville group: Cincinnati, Ohio. 



