PLATE XL VI. 



(Figures 1-5 by E. P. Whitfield; 6, 10, 16, K-at by G. B. Simpson; 7-9, 11-21, 25-28 by E. Emmons.) 



Legend : p. Filling; of pedicle-cavity. l a. Anterior adductors. 



t. Teeth. a'. Posterior adductora. 



d. Dental lamellae. vc. Cast of viscei-al foramen. 



C8. Cardinal margin. " hp. Cast of hinge-plate. 



r. Diductor scare. 



Genus ATHYRIS, McCoy. 



Page 83. 

 See Plate 45. 



Athykis polita, Hall. 



Fig. 1. A venti-al view of an internal cast; showing the filling of the rostral cavity and the muscular 



impressions. 

 Fig. 2. Doreal view of the same specimen. 



Figs. 3-5. Profile, doi-sal and ventral views of a specimen retaining the external surface. 

 Chemung group. Steuben county, JV. Y. 

 This species has more the contour of shells which have been placed under the subgenus Sbmi- 

 vvjji, than of the true Athyris. Should its surface prove to be devoid of free lamellse, it 

 would naturally fall into that group. 



Athybis DENSA, sp. IIOV. 



Fig. 6. The interior of a small but thickened and entire pedicle-valve ; showing the broad cardinal sur- 

 faces, the deep pedicle-cavity and the relatively large muscular impressions which extend 

 almost to the anterior margin of the valve. 



St. Louis gi-oup. Colesburgh, Kentucky. 

 Fig. 7. The interior of a larger pedicle-valve ; showing the thickening in the umbonal region and the 



division of the muscular area by a prominent ridge. 

 Fig. 8. The interior of a pedicle-valve with broader cardinal margins than the preceding specimens, and 

 retaining the median ridge, but with the muscular area obscure. 

 St. Louis group. WasMngton county, Indiana. 

 Figs. 9, 10. Profile and dorsal views of conjoined valves ; showing the contour of the shell, the foramen 

 and broad cardinal slopes of the pedicle-valve, the median elevation and low marginal sulcus 

 of the brachial valve. 



St. Louis group. Colesburgh, Kentucky. 

 Fig. 11. The interior of a pedicle- valve, with a relatively small muscular area, and a linguate extension 

 of the anterior margin which is much foreshortened in the figure. 

 St. Louis group. Lanesville, Indiana. 

 Fig. 12. The interior of a pedicle-valve ; showing in fuller detail the structural features. 

 St. Louis group. Colesburgh, Kentucky. 



Athyris Hannibalensis. Swallow. 



Fig. 13. A dorsal view of the exterior of conjoined valves ; showing the highly lamellose surface. 

 Fig. 14. The exterior of a i>edicle-valve ; showing the bases of the free lamellae, and the low median sinus. 

 Fig. 15. The interior of a pedicle-valve ; showing the character of the muscular area. 

 Choteau limestone. Louisiana, Missouri. 



Athyris lamellosa, L6 veil 16. 



Fig. 16. The ventral side of an internal cast of conjoined valves ; showing the striated scar of the pedicle- 

 muscle, the cordate and sharply defined adductor scars, and the faintly outlined diductors. 

 Near the anterior margin is a portion of one of the broad concentric lamellae. 



Fig. 17. The opposite side of the same specimen ; showing the peculiar form and division of the adductor 

 acars, and a portion of one of the concentrically striated free lamellae. 

 Waverly group. SdotoviUe, Ohio. 



