PLATE XXV. 



(Figures 1-8 by F. B. Meek; 9-16, 22-24, 26-31 by K. P. Whitfield; 17-21, 25, 32-35 by E. Emmons.) 



Legend : A- Delthynum. j. Cardinal process. 



Dg. Deltidial groove. b. Dental sockets. 



b'. Apical callosity or tube. c. Socket-walls. 



, 8. Median septum. a. Anterior adductors. 



d. Dental lamella. a'. Posterior adductors. 



Genus CYRTINA, Davidson. 



Pa(?c 43. 



Cyrtina kostrata, Hall. 



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. 



Pigs. 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 the pedicle-valve, looking into the umbonal cavity ; showing the convergent dental 



lamellse, their union with the median septum, and the tubular edge of the latter. 

 Oriskany sandstone. Albany county, N. ¥., and Oiunberland, Md. 



Genus SPIRIFER, Sowerby. 



Page I. 



Spirifer Macbridii, Calvin. 



Fig. 9. The exterior of a brachial valve. 



Pig. 10. The exterior of a pedicle- valve, somewhat foreshortened ; showing the faint plication in the sinus. 



Pig. 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 compof^ition 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 brachial valve retaining the spiral cones ; showing their position, number of 

 volutions and the anterior portion of the long crura. 



Figs. 15, 16. Etdargementa of the surface ; the former from the lateral plications, the latter from the median 



sinus. 



Hamilton group. HocJcford, lorwa. 



Spirifer sp., coin|)arc S. Macbuidii, Calvin. 



Pig8. 17, 18. Views of the exterior of a 8j)ecimen, with two low, broad plications on the median sinus, and 

 having a somewhat diffei-ent asiiect than normal examples of (S. Macbridii. 



Fig. 19. An enlargement of the surface, which is covei-eil with radiating rows of elongate pustules, distinctly 

 coarser than in <S. Macifridii. 



Hamilton group. Probably from the blue shales at Hod Island, Illinois. 



Spirifer asper, Hall. 

 Fig. 20. The front view of a, normal individual. 

 Fig. 21. The exterior of a brachial valve. 



Hamilton group. Neio 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 inner side ; showing the incipient stage of the canaliferous tube of Strinooththis. 

 Fig. 24. An enlargement of the surface. 



Hamilton group. Rockfurd, loita. 

 Pig. 25. The exterior of a pedicle-valve, probai)ly representing this species. 



Hamilton group. Canandaigua, N. Y. 



