PLATE LXXIX. 



(Figures 1-20, 2i-24. 2ii, HO, 40 12 liy 1{ 1'. WiriTKirxD; 21, 28.3(>-38 by O.K. Simpson; 25-27, .U-M, 39 by K. Emmons ) 



Genus CENTKONELLA, Billings. 



rase 265. 

 C'ENTHONEI.LA GLANS-FAGEA, Hull. 



Fig-. 1. Dorsal vii'w of :i lai-g-e individual. 



Figs. 2 -4. Doi-sal, V(?ntral and jirolile views of a small specimen, havinff a more elong-ate outline than the 

 preceding ; .showing the convexo-concave contour. X 3. 

 Schoharie grit. A/bany comity, Neio Ymk. 

 ¥\^. 5, t). Dorsal and pnitile views of a very ventricose individual having the elevated character of 

 C. tumida, Billings, but of smaller size. 



Corniferous limestone. Cayuga, Ontario. 

 Fig. 7. An internal cast ; showing impressions of the hinge-i)late, dental sockets and mnscular scars of 

 the brachial valve. X 2. 



Schoharie grit. Albany co%mty. New Ymh. 

 Fig. 8. Dorsal view of a specimen having the brachial valve quite Hat. X 2. 

 Corniferous limestone Drift, near Ann Arbor, Michigan. 

 Figs. 9, 10. Protile and inner views of the loop and its attachment ; showing the di\-ided hinge-plate and 

 the narrow anterior expansion of the loop with its median I'idge. X 5. 

 Corniferous limestone. Tl'f.v/ertt New Tork. 

 Figs. 11, 12. Dorsal and protile views of a \ery gibbous shell, which shows the foramen and deltidial plates. 



Corniferous limestone. Drift, near Ann Arbm, 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. Doi-sal view of an internal cast ; showing the muscular scars and the impression of the hinge- 

 plate. X 2. 



Corniferous 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 scarb. X 3. 



Corniferous limestone. Cayuga, Ontario. 



Centronella Hecate, Billings. 



Fig. 15. Doreal 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. 



Centuonella impressa, Hull. 



Fig. It). 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 \-alve ; showing the divided hinge-plate, the elongate muscular scars 



and the vascular sinuses. X 2. 



Hamilton shales. Bellona, New York. 



Centuu.vella alveata. Hall. 



Figs. 22-24. Doi'sal, protile and ventral views of the original specimen ; showing the large size, elongate 

 form and deep median fold and sinus. 



Onondaga limestone. Locality .' (New York). 



