PLATE XXVIII. 
(Figures 1, 48, 49 copies; 2-5, 8-13, 15, 21-29, 31-33, 43, 50, 52 by R. P. Whitfield; 6, 7,14, 16-20, 30, 34-42, 44-47, 51, 
53, 54 by E. Emmons. 
Legend: 
D. Deltidium. 
F. Foramen, 
d. Dental lamellse. 
s. Median septum, 
s'. Callosity in delthyi-ium. 
T. Tubular edge of the median septum, 
j. Cardinal pi-ocess. 
b. Dental sockets. 
c. Socket-walls. 
Genus CYRTIA, Dalman. 
Page 40. 
Cyrtia rxporrecta, Wahleiiliei'g. 
Fig. 1. The exterior of a normal example. (Aftei' Davidson.)] 
Figs. 48, 49. (On bottom line of jdate.) Enlai-ged views; showing the deltidial covering, foramen and elon¬ 
gate foraminal gi'oove. In tig. 49 the foi-amen has been normally or casually closed. (After 
Davidson.) 
Fig. 51. Transverse section of the umbonal region ; showing the dental lamellae resting on (he bottom of 
the valve and the thickening at their union with the deltidial covering. 
Wenlock limestone. England. 
Cyrtia exporrecta, Wahleiiborg, viir. arrecta, Hall and Whitfield. 
Figs. 2, 3. Cardinal and profile views of the oi-iginal specimen. 
Niagara group. Louisville, Kenluckg. 
Cyrtia radians, sp. uov. 
See Plate 21. 
Figs. 4, 5. Cardinal and front views of a small example ; showing the finely radiate-lineate exterior. 
Figs. 50, 52. (On bottom line of plate.) The central cardinal area of two examples ; showing the direct, 
cii'cular foramen and the elongate foraminal groove. X 3. 
Clinton group. Rochester, N. Y. 
Genus CYR'ITNA, Davidson. 
Page 43. 
Cyrtina rostrata, Hall. 
See Plate 25. 
Fig. 6. The interior of a pedicle-valve; showing the junction_of the dental lamella; with the median sejitum. 
Oriskany sandstone. Cumberland, Maryland. 
Cyrtina bipeicata, Htdl. 
Fig. 7. A view of the pedicle-valve of a silicified internal cast; showing a portion of one of the spirals. 
Corniferous limestone. Drift at Ann Harbor, Michigan. 
Fig. 8. A cardinal view of conjoined valves ; showing the imperforate deltidium. 
Figs. 9, 10. Front and dorsal views of the same specimen. 
Schoharie grit. Schoharie, N. Y. 
Cyrtina curvilineata, White. 
Fig. 11. A view of a large specimen ; showing the plicated median fold of the brachial valve, and the dis¬ 
torted umbo of the opposite valve. 
Fig. 12. A profile of the same specimen. 
