PLATE XXV. 



(Kiftures 1-8 by F. B. Mkkk; U-IC, 22--24, 2ii-31 by U. P. Wuitkield; 17-'.;1, 25, 32-35 by E. EMMONS.) 



Le^tnii : i\. Delthj rium. j. Cardinal process. 



Dg-. Deltiiiiiil groove. b. Dental sockets, 



s'. Apical callosity or lube. c. Socket-walls, 



s. Median septnni. a. Anterioi' addudors. 



d. Dental JaToell!!'. a'. Posterior adductors. 



Genus CYRTINA, Davidson. 



ra^c 43. 

 Cyrtina KOSTRATA, Iltlll. 

 Fig. 1. A front view of a specimen .somewhat below average size. 



2. A cardinal view of the same; showing the tubular edge of the median septum within the delthyrium. 

 A bi'achial valve of a larger example. 

 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. 

 The interior of a brachial valve. 



The interior of the pedicle-valve, looking into the umbonal cavity ; showing the convei'gent dental 

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

 Oriskany sandstone. Albany comity, N. Y., and Cuinberland, Md. 



Genus SPIRIFER, Sowerbv. 



I'Mge 1. 



Spirifer Macbridii, C'alviii. 



Fig. 9. The exterior of a brachial valve. 



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



Fig. 11. A carilinal 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 musculai' 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 retaining the spiral cones; showing their position, number of 

 volutions and the anterior portion of the long crura. 



Figs. 15, 16. Enlargements of the surface ; the former fi'om the lateral i>lications, the latter iVom the median 

 sinus. 



Hamilton group. Mockford, Iowa. 



Si'iKiFER s;)., coinp.iri! S. Macbridii, Calvin. 



Figs. 17, IS. Views of the exterior of a sjiecimen, with two low, bioad plication.-; iin the median sinus, and 

 having a somewhat different aspect than normal examples of S. Macbridii. 



Fig. 19. An enlargement of the surface, which ia covered with radiating rows of elongate pustules, distinctly 

 coarser than in iS. Macbridii. 



Hamilton gi'oup. Probably from the blue shales at Mod Ls'land, Illinois. 



SpnUB'ER ASl'ER, Hall. 

 Fig. 20. The fi-ont view of a normal individual. 

 Fig. 21. The exterior of a brachial valve. 



Hamilton gi'oup. NeiB Buffalo, Iowa. 

 Fig. 22. A pedicle-valve viewed from at)ove. 



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 Syrimgothtris. 

 Fig. 24. An enlargement of the surface. 



Hamilton group. Rockford, Iowa. 

 Fig. 25. The exterior of a pedicle-valve, pi'obably representing this species. 



Hamilton grouji. Canandaigua, N. T. 



