PLATE XXIV. 



(Figures 1-J7 hy K. 1'. Whiti ield. I 



Legend: A- Delthyrium. '>• Dental Bockets. 



I). Deltiiiiiim. c'. Socket-walls. 



Dg-. Deltidial grooves. a. Anterior aildnctors. 



t. Teeth. a'. Postei'ior adductors, 



s'. Ajiical callosity. r. Diductors. 

 j. Cardinal process. 



Genus SPIRIFER, Soweury. 



rage 1. 



Spirifek audaculus, Coiuail. 



Fig. 1. A small individual of normal proportions. 



Fig. 2. A brachial valve of an average example. 



Fig. 3. The pedicle-valve of a rotnnd specimen. 



Figs. 4, 5. Dorsal and profile views of an individual with short hinge and fewer plications. 



Fig. 6. Front view of an average adult. 



Fig. 7. The inteiior of the brachial valve ; showing the aiticnlating apparatus and muscular scars. 



Fig. 8. A cardinal portion of a larger brachial valve ; showing the same strui-turea more distinctly. 



Fiu-. 9. The intei'ior of a pedicle-valve ; showing the formation of the apical callosity, and the character of 

 the muscular area. 



Fig. 10. The central portion of the cardinal area of the pedicle-valve, retaining the remnants of the ilel- 

 tidial covering. X 2. 



Fig. 11. A similar view of another example ; showing the high development of the delthyi-ial callosity. 



Fig. 12. A part of the brachial valve ; showing the cardinal process, articulating ajiparatus and the char- 

 acter of the adductor scars. X 2. 



Pig. 13. An enlargement of the extei-n.il surface ; showing the grooves on the summits of the plications. 

 Hamilton shales. Western New York. 



Spirifek angustus, Hall. 



Figs. 14, 15. Dorsal and ventral views of the exterior of a rather large imlividual. 



Fig. 16. A cardinal view of the same specimen. 



Fig. 17. An enlargement of the external surface ; showing the flattened plications and incipient grooves. 



Spirifer audaculus, v.'ir. macronotus, Hall. 



Fig. 18. A cardinal view of a large individual which retains the deltidial covering in a broken condition. 



Fig. 19. A cardinal view of a shallower, more extemled individual. 



Fig. 20. A protile view of the same. 



Fig. 21. A view of the interior of the pedicle-valve, looking into the unibonal cavity ; showing the callosity 

 and dental plates. 



Fig. 22. Central portion of the cardinal area; showing the highly developed delthyi'ial callosity. X 2. 



Fig. 23. A similar view of another specimen in which the deltidial covering is retained in a broken con- 

 dition. 



Fig. 24. The interior of a part of the pedicle-valve ; showing the divisions of the muscular area, and the 

 thickened dental ridges. 



Fig. 2.'5. The interioi' of a similar specimen, the apex being removed to show more clearly the details of 

 the muscular impression. 



Figs. 26, 27. Enlargements of the external surface ; showing characters which are often seen on the same 

 shell. 



HaLiilton shales. Wester7i Neio YwJc. 



