PLATE XXV. 
(Figures 1-8 by F. B. Meek; 9-16, 22-24, 26-31 by R. P. Whitfield; 17-21, 25, 32-35 by E. Emmons.) 
Legend : A- Delthyrium. j. Cardinal yirocess. 
Dg. Deltidial groove. b. Dental sockets, 
s'. Apical callosity or tube. c. Socket-walls, 
s. Median septum. a. Anteiior adductors, 
d. Dental lamellae. a'. Posterioi- adductors. 
Genus CYRTINA, Davidson. 
Page 43. 
CyR'J'INA nOSTRATA, ILlll. 
Fig. 1. A front view of a specimen somewhat below average size. 
Fig. 2. A cardinal view of the same; showing the tubular edge of the median septum within the delthyrium. 
Fig. 3. A brachial valve of a larger example. 
Figs. 4, 5, 8. Views of an old shell, much thickened about the margins of the valves. Fig. 8 shows the 
edge of the median septum within the delthyrium. 
Fig. 6. The interior of a brachial valve. 
Fig. 7. The interior of Ihe pedicle-valve, looking into the umbonal cavity ; showing the convei'gent dental 
lamellae, their union with the median septum, and the tubular edge of the lattei-. 
Oriskany sandstone. Albany county, N. Y., and Cumberland, Md. 
Genus SPIRIFER, Sowerby. 
Page ]. 
Spirifer Macbridii, Calvin. 
Fig. 9. The exterior of a brachial valve. 
Fig. 10. The exterior of a pedicle-valre, somewhat foreshortened ; showing the faint plication in the sinus. 
Fig. 11. A cardinal view ; showing the elevation of the area, and the degree of development of the apical 
callosity. 
Fig. 12. The central cardinal portion of the interior of a brachial valve ; showing the articulating appara¬ 
tus and the composition of the muscular area. X 2. 
Fig. 13. The interior of a pedicle-valve ; showing the development of the dental plates. 
Fig. 14. The interior of a bi-achial valve I'etaining the spiral cones; showing their position, number of 
volutions and the antei-ior portion of the long crura. 
Figs. 15, 16. Enlargements of the surface ; the former fi'om the lateral plications, the latter from the median 
sinus. 
Hamilton group. Rockford, Iowa. 
Spirifer sp.. coiiipure S. Macbridii, Calvin. 
Figs. 17, 18. Views of the exterior of a specimen, with two low, broad plications on the median sinus, and 
having a somewhat different aspect than normal examples of iS. Macbridii. 
Fig. 19. An enlargement of the surface, which is covered with radiating rows of elongate pustules, distinctly 
coarser than in S. Macbndii. 
Hamilton group. Probably from the blue shales at Rock Island, Illinois. 
Spirifer asper, Hall. 
Fig. 20. The front view of a normal individual. 
Fig. 21. The exterior of a bi-achial valve. 
Hamilton group. Nexo Buffalo, Iowa. 
Fig. 22. A pedicle-valve viewed from above. 
Fig. 23. The cardinal view of a pedicle-valve with highly developed delthy rial callosity; the central extension 
concave on the innei- side; showing the incipient stage of the canaliferous tube of Syeingothyris. 
Fig. 24. An enlargement of the surface. 
Hamilton group. Rockford, Iowa. 
Fig. 25. The exterior of a pedicle-valve, probably representing this species. 
Hamilton group. Canandaigua, N. Y. 
