PLATE XXXIX. 



(Figures 1-20, 2i-24, 29, SO, 40-)2 by K. P. Whitfif.ld; 21 , i8,.36-38 by G. B. Simpson; 23-27, 31-35, 39 hy E. EHHON8.) 



Genus CENTK0N1':LLA, Billings. 



Page 265. 



Centronella glans-fagea, Hall. 



Fig. 1. Dorsal view of a large imlividual. 



Figs. 2 -4. Doi-sal, ventral anil profile views of a small specimen, having- a more elongate outline than the 

 preceding ; showing the convexo-concave contour. X 8. 

 Schoharie grit. Albany county. New York. 

 Pigs. 5, 6. Dorsal and profile views of a very ventricose individual having the elevated character of 

 C. tumida, Billings, but of smaller size. 



Comiferous limestone. Cayuga, Ontario. 

 Fig. 7. An internal cast ; showing impressions of the hinge-plate, dental siwkets and muscular scars of 

 the brachial valve. X 2. 



Schoharie giit. Albany county. New York. 

 Fig. 8. Doreal view of a specimen having the brachial valve quite flat. X 2. 

 Comiferous limestone Dr\ft, 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 antei-ior expansion of the loop with its median ridge. X 5. 

 Comiferous limestone. Wextem New York. 

 Pigs. 11, 12. Dorsal and profile views of a very gibbous shell, which shows the foramen and deltidial plates. 



Comifei'Ous limestone. Drift, near Ann Arbor, Michigan. 

 Fig. 13. An intemal cast of the pedicle-valve ; showing the impressions of the teeth and the deep scai- of 

 the_-pedicle-muscle. the anterior extremity of which is enclosed by the dJductor scars. X 2. 

 Schoharie grit. Albany county. New York. 

 Fig. 14. Doreal view of an internal ca.st ; showing the muscular scars and the impression of the hinge- 

 plate. X 2. 



Comiferous 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 seal's. X 3. 

 Fig. 21. The interior of a brachial valve; showing the hinge-plate and the variation in the form of the 

 muscular scai-s. X 3. 



Comiferous limestone. Cayuga, Ontario. 



Centronella Hecate, Billings. 



Fig. 15. Dorsal view of a specimen ; showing the elongate form and general similarity to C. impressa. Hall, 

 with which it may be identical. 



Comiferous limestone. Caynga, Ontario. 



Centronella jmpressa, 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. BelloiM, New York. 



Centuo.nella ALVEATA, Hilll, 



Piga. 22-24. Doi-sal, pi-otte and ventral views of the original specimen ; showing the large size, elongate 

 form and deep median fold and sinus. 



Onondaga limestone. Locality 1 (New York). 



