PLATE XXXVIII. 



(Pigs. 1-8, U-IS, 15-19 by K. P. Whitfield; 9, 10, 14 by Q. B. Simpson ) 



Genus SPIKIFEK, Sowkrby. 



Page 1. 



Spirikkr MODESTUS, Hilll. 



Vig. 1. A silicified example ; showing the usual condition of the exteiior, and the absence of any defined 



cai-dinal area. X 2. 

 Fig. 3. The intei-ior of a portion of the pedicle-valve ; showing the form of the muacalar area. 

 Lower Helderberg group. Outnberland, Maryland. 



Spibifeb lineatus, Martin. 



Figs. 3, 4. Two views of a small specimen ; showing the form and usual condition of the surface. 

 Fig. 7. An enlargement of the surface ; showing the spine-bases along the growth-lines. 

 Fig. 8. An enlargement of the cardinal area of the specimen represented in fig. 4 ; showing the incipient 

 development of the deltidial plates and limitation of the cardinal area. 

 Coal Measures. Ivwa. 



Spirifer Maia, Billings. 



Figs. 5, 6. Two individuals, showing slight variations in length of hingfe and marginal outline. 

 Corniferous limestone. Near Columbus, Ohio. 



Spirifer fimbbiatus, Conrad. 



See plate 36. 

 Fig. 9. An enlargement of a portion of the exterior ; showing the long, medially grooved and divided 



surface-spines, with their lateral spinules. X 3. 

 Fig. 10. A thin section of these compound spines ; showing their interior filling and the lateral spinules. X 3. 

 Hamilton shales. Canandxiigiiri Lake, N. T. 



Spirifer l^vis, Hall. 



Fig. 11. A canlinal view of the pedicle-valve ; showing the completed deltidial covering. 

 Fig. 12. Exterior of a )>edicle-valve ; showing faint lateral undulations. 



Fig. 13. An internal cast of the pedicle-valve ; showing the impression of the muscular area and ovarian 

 markings. 



Portage group. Ithaca, N. T. 



Spirifer hirtus, White and Wiiitfield. 



Fig. 14. An enlargement of the surface ; showing the concentric rows of spine-bases, each of which retains 

 the remnant of the median partition dividing it into two chambera. X 5. 

 Kinderhook group. Illinois. 



Spirifer divaiucatus, Hall. 



FigR. 15-17. Front, dorsal and profile views of an entire individual of normal adult size ; showing the rela- 

 tively short hinge, high area, low fold and sinus, and the even plication of the entire surface. 

 Hamilton group. York, N. Y. 



Spirifer Mortonanus, Miller (=S. fastigatus, Meek and Worthen). 



Fig. 18. The pedicle-valve of a large individual. 



Fig. 19. Internal cast of a {)edicle-valve ; showing the veKical striation of the cardinal area, the impression 

 of the muscular area and the ovavian markings. 



Keokuk group. Craxt^ordtvilU, Indiana. 



