PLATE XXVIII. 



(Figare8 I, 48, 49 copies; WS, 8-13, 15, 21-29, 31-33, 4.!, 50, 5; by R. P. Whitfield; «, 7, 14, 18-20, 30, J4-42, 44-47, SI, 



53, 54 by E. Emmons. 



Legend : D. Deltidiam. 

 F. Foramen. 

 <1. Dental lamellse. 

 8. Median septum, 

 s'. Callosity in delthyrium. 



T. Tubular edge of the median septum, 

 j. Cardinal process. 



b. Dental sockets. 



c. Socket-walls. 



Genus CYRTIA, Dalman. 



Page 40. 



Cyrtia exporrecta, W'ableiil)cig. 



Fig. 1. The exterior of a normal example. (After Davidbon.)! 



Figs. 48, 49. (On bottom line of plate.) Enlarged views; showing the deltidial covering, foramen and elon- 

 gate foraminal groove. In 6g. 49 the foramen has been normally or casually closed. (After 

 Davidson.) 

 , Fig. 51. Transveree section of the umbonal region ; showing the dental lamella resting on Ihe bottom of 

 the valve and the thickening at their union with the deltidial covering. 

 Wenlock limestone. England. 



Cyrtia exporrecta, Walileiil)cig, Viir. arrecta, Hall and WhitfielcK 



Figs. 2, 3. Cardinal and profile views of the original specimen. 

 Niagara group. Louisville, Kentucky. 



Cyrtia radians, sp, nov. 



See Plate 21. 

 Figs. 4, 5. Cardinal and front views of a small examjile ; showing the finely radiate-Iineate exterior. 

 Figs. 50, 52. (On bottom line of plate.) The central cai-dinal area of two examples; showing the direct, 

 circular foramen and the elongate foraminal groove. X 3, 

 Clinton gfi-oup. Rochester, N. Y. 



Fig. 



Fig. 



Fig. 

 Pig". 



Fig. 

 Fig. 



Genus CYRTINA, Davidson. 



Page 43. 



Cyrti.va rostrata, Hall. 



See Plate 25. 



6. The interior of a pedicle-valve; showing the junction,of the dental lamellte with the median septum. 



Oriskany sandstone. Cumberland, Maryland. 



Cyrtina biplicata, Hall. 



7. A view of the pedicle-valve of a silicified internal cast ; showing a portion of one of the spirals. 



Coi-niferous limestone. Di-ift at Ann Harbor, Michigan. 



8. A cardinal view of conjoined valves ; showing the imperforate deltidium. 



9. 10. Front and dorsal views of the same specimen. 



Schoharie grit. Schoharie, N. Y. 



Cyrtina curvilineata, White. 



11. a view of a large sjtecimen ; showing the plicated median fold of the brachial valve, and the dis- 



torted umbo of the opposite valve. 



12. A profile of the same specimen. 



