PLATE XXIII. 



(Figures 1-18 by H. I". Whitfield.) 



Legend ; A. Cardinal area, pedicle-valve, 



a'. Inner division, pedicle-valve. 



&". Outer division, pedicle-valve. 



F. Delthyrium. 



s'. Apical callosity. 



d. Dental lamellee. 



X. Pedicle-cavity. 



Gknus SPIRIFER, Sowerby. 



Page 1. 



Spirifer granulosus, Conrad. 



Fig. 1. Dorsal view of a normal adult, retaining the shell. 



Fig. 2. The interior of a pedicle-valve ; showing the apical callosity in the delthyrium and the character 

 of the muscular area. 



Fig. 3. The interior of a brachial valve ; showing the articulating apparatus and muscular area. 



Fig. 4. An enlargement of the surface ; showing the papillose character of the shell. 



Fig. 5. The central i)Oition of a cast of the brachial valve; showing the striated cardinal process and the 

 two pairs of adductor scars. X 2. 



Fig. 6. A similar view of another specimen. 



Fig. 7. A cast of the muscular area of the pedicle-valve with the muscular impression unusually elongate. 



Fig. 8. A similar view of a larger specimen. 



Fig. 9. Another view of the same parts, the muscular area being proportionally shorter and smaller than 

 in the preceding tigure. 



Fig. 10. A view of the same charactei'S in another example. All these sjiecimens show variations in the 

 form of the niusculai' area, the size of the adductor scars as well as diflerent degrees of devel- 

 opment of the callosity of the delthyrium. 



Fig. 11. A portion of the muscular area of the pedicle-valve ; showing its surface markings and the dis- 

 tinction between the diductor and adductor scars. X 2. 



Fig. 12. A profile of an internal cast of the pedicle-valve ; showing the tilling of the rostral and muscular 

 cavities. 



Fig. 13. Similar cast of another pedicle-valve with a more elevated muscular impression. 



Fig. 14. An enlargement of a partly exfoliated surface. 



Hamilton shales. Western New York. 



Fig. 15. An enlargement of a worn surface. The coai'se punctations are not structural but probably due 

 to some boring sponge. 



Hamilton group. Cumberland, Maryland. 



Spirifer macrothyris, Hiill. 



Fig. 16. The exterior of a full-grown individual. 



Fig. 17. A cardinal view of an imperfect specimen ; showing the elevation of the valves. 

 Fig. 18. An enlai'gement of the surface ; showing the crenulate margins of the concentric lamellsB. 

 Corniferous limestone. Near Columbus, Ohio. 



