PLATE LXXIX. 
(Figures 1-20, 22-24, 29, 30, 40-42 by K. P. Wiiitfikld; 21,28, 36-38 by G. B. Simpson; 25-27, 31-35, 39 by E. Emmons.) 
Genus CENTliONP^LLA, Billings. 
Page 265. 
Centronella glans-fagea, Hall. 
Fig. 1. Dorsal view of a larg-e individual. 
Figs. 2 -4. Dorsal, ventral and profile views of a small specimen, having a more elongate outline than the 
preceding ; showing the convexo-concave contour. X 3. 
Schoharie grit. Albany coionty. New Ycn-k. 
Figs. .5, 6. Dorsal and profile views of a very ventricose individual having the elevated character of 
C. tuonida, Billings, but of smaller size. 
Corniferous limestone. Cayuga, Ontario. 
Fig. 7. An internal cast; showing impressions of the hinge-plate, dental sockets and muscular scars of 
the brachial valve. X 2. 
Schoharie gi-it. Albany coxinty. New York. 
Fig. 8. Dorsal view of a specimen having the brachial valve quite flat. X 2. 
Corniferous limestone. Drift, near Ann Arbor, Michigan. 
Figs. 9, 10. Profile and inner views of the loop and its attachment; showing the divided hinge-plate and 
the narrow anterior expansion of the loop with its median ridge. X 5. 
Corniferous limestone. Western New York. 
Figs. 11, 12. Dorsal and profile views of a very gibbous shell, which shows the foramen and deltidial plates. 
Corniferous limestone. Drift, near Ann Arbor, Michigan. 
Fig. 13. An internal cast of the pedicle-valve ; showing the impressions of the teeth and the deep scar of 
the-pedicle-muscle. the anterior extremity of which is enclosed by the diductor scars. X 2. 
Schoharie grit. Albany county. New York. 
Fig. 14. Dorsal view of an internal cast; showing the musculai- scars and the impression of the hinge- 
plate. X 2. 
Cornifei'ous limestone. Drift, near Ann Arbor, Michigan. 
Fig. 17. The interior of the umbonal portion of the brachial valve ; showing the thickened divisions of the 
hinge-plate and the adductor scars. X 3. 
Fig. 21. The interior of a brachial valve ; showing the hinge-plate and the variation in the form of the 
muscular scars. X 3. 
Corniferous limestone. Cayuga, Ontano, 
Centronella Hecate, Billiiiws. 
Fig. 15. Dorsal view of a specimen ; showing the elongate form and general similarity to C. impressa. Hall, 
with which it may be identical. 
Corniferous limestone. Cayuga, Ontario. 
Centronella impressa, Hall. 
Fig. 16. Dorsal view of an average individual; showing the form and concave brachial valve. 
Fig. 18. The interior of the pedicle-valve, retaining the deltidial plates and teeth. 
Fig. 19. The interior of a brachial valve ; showing the greatly thickened divisions of the hinge-plate, and 
the minute cardinal process. 
Fig. 20. The interior of a brachial valve; showing the divided hinge-plate, the elongate muscular scars 
and the vascular sinuses. X 2. 
Hamilton shales. Bellona, New Ycnk. 
Centronella alveata, Hall, 
Figs. 22-24. Dorsal, prohle and ventral views of the original specimen ; showing the lai-ge size, elongate 
form and deep median fold and sinus. 
Onondaga limestone. Locality ? {New York). 
