PLATE XXXVIII. 



(Figs, 1-8, 11-13, 16-19 by U. P. Wihtfiei.d; 9, 10, 14 by G. B. SisirsoN ) 



Genus SPIKIFEK, Sowerby. 



Page 1. 



Spiriker modestus, Hall. 



Fii'. 1. A silii'itieii example ; .'showing the usual condition of the exterior, ami the absence of uuy defined 



cardinal area. X '2. 

 Fi"'. 3. The interior of a poi'tion of the pedicle-valve ; showing- the form of the nmscular area. 

 Lower Helderberg group. Cumberland, Maryland. 



Spirifer lineatus, Martin. 



Figs. 2, 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 gi-owth-lines. 

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

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

 Coal Measures. Imoa. 



. Spirifer Maia, Billings. 



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

 Corniferous limestone. Near Cvluiiibus, Ohio. 



Spirifer fimbriatus, Ci)nracl. 



See plate 36. 

 Fig. 9. An enlargement of a portion of tlie exterior ; showing the long, medially gi'ooved and divided 



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

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

 Hamilton shales. Caiiandaigm Lake, N. Y. 



Spirifer l^vis, Hall. 



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

 Fig. 12. Kxterior of a pedicle-valve; showing faint lateral undulations. 



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

 mai'kings. 



Portage group. Ithaca, N. T. 



Spirifer iiirtus. Wi;ile uinl Wliitticld. 



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

 the i-emnant of the median partition dividing it into two chambers. X 5. 

 Kinderhook group. Illinais. 



Spirifer divaricatus, Hall. 



Figs. 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 Wortiicn). 



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



Fig. 19. Internal cast of a pedicle-valve ; showing the vertical striation of the cardinal area, the impression 

 of the muscular area and the ovarian markings. 



Keokuk gi'oup. Crawfordsville, Indiana. 



