PLATE XXIV. 
(Figures 1-27 by R. 1*. Whitfield.) 
A. 
Delthyrium. 
b. 
Dental sockets. 
D. 
Deltidium. 
c'. 
Socket-walls. 
Dg. 
Deltidial gi-ooves. 
a. 
Anterior adductors. 
t. 
Teeth. 
a'. 
Posterior adductors. 
s'. 
Apical callosity. 
r. 
Diductors. 
j- 
Cardinal process. 
Genus SPIRIFER, Sowerby. 
Page 1. 
Spirifek audaculus, Connul. 
Fig-. 1. A small individual of nonnal proportions. 
Fig. 2. A brachial valve of an average example. 
Fig. 3. The pedicle-valve of a rotund specimen. 
Figs. 4, 5. Dorsal and profile views of an individual with short hinge and fewer plications. 
Fig. 6. Fi-ont view of an average adult. 
Fig. 7. The interior of the brachial valve ; showing the articulating apparatus and muscular scai-s. 
Fig. 8. A cardinal portion of a largei- brachial valve ; showing the same structures more distinctly. 
Fig. 9. The interior of a pedicle-valve ; showing the formation of the apical callosity, and the character of 
' the muscular area. 
Fig. 10. The central poi-tion of the carilinal area of the pedicle-valve, retaining the remnants of the del- 
tidial covering. X 2. 
Fig. 11. A similar view of another example ; showing the high development of the delthyrial callosity. 
Fig. 12. A part of the brachial valve ; showing the cardinal process, articulating apparatus and the char¬ 
acter of the adductor scars. X 2. 
Fig. 13. An enlargement of the external surface ; showing the grooves on the summits of the plications. 
Hamilton shales. Western New York. 
Spirifek angustus, Hall. 
Figs. 14, 15. Dorsal and ventral view’s of the exterior of a rather large individual. 
Fig. 16. A cardinal view of the same specimen. 
Fig. 17. An enlargement of the external surface ; showing the flattened jilications and incipient grooves. 
Spirifer audaculus, var. 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 extended individual. 
Fig. 20. A profile view of fhe same. 
Fig. 21. A view of the interior of the pedicle-valve, looking into the umbonal cavity ; showing fhe callosity 
and dental jilates. 
Fig. 22. Central portion of the cardinal area; showing the highly developed delthyrial 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. 25. The interior 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. 
Hamilton shales. Western New York. 
