PLATE XL VI. 
(Figures 1-5 by R. P. Whitfield; 6,10,15, 32-21 by G. B. Simpson; 7-9,11-21, 25-28 by E. Emmons.) 
Legend ; p. Filling of pedicle-cavity, 
t. Teeth. 
d. Dental lamellse. 
cs. Cardinal margin, 
r. Diductor scars. 
a. Anterior adductors, 
a^. Posterior adductors. 
VC. Cast of visceral foramen, 
hp. Cast of hinge-plate. 
Genus ATHYEIS, McCoy. 
Page 83. 
See Plate 45. 
Athyris polita, Hall. 
Fig. 1. A ventral view of an internal cast; showing the filling of the rostral cavity and the muscular 
impressions. 
Fig. 2. Dorsal view of the same specimen. 
Figs. 3-5. Profile, dorsal and ventral views of a specimen retaining the external surface. 
Chemung group. Steuben county, N. Y. 
This species has more the contour of shells which have been placed under the subgenus Semi- 
NULA, than of the true Athyris. Should its surface prove to be devoid of free lamellie, it 
would naturally fall into that group. 
Athyris densa, sp. nov. 
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 group. Colesbwgh, 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. Washington 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. 
A dorsal view of the exterior of conjoined valves ; showing the highly lamellose surface. 
The exterior of a pedicle-valve; showing the bases of,the free lamellse, and the low median sinus. 
The interior of a pedicle-valve ; showing the character of the muscular area. 
Choteau limestone. Louisiana, Missouri. 
Athyris lamellosa, Leveill6. 
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 lamellse. 
Fig. 17. The opposite side of the same specimen ; showing the peculiar form and division of the adductor 
scars, and a portion of one of the concentrically striated free lamellse. 
Waverly group. Sciotoville, Ohio. 
Fig. 13. 
Fig. 14. 
Fig. 15. 
