PLATE XXXVIII. 
(Figs. 1-8,11-13,15-19 by R. P. Whitfield; 9,10,14 by G. B. Simpson ) 
Genus SPIRIFEK, Sowekby. 
Page 1. 
Spirifer modestus, Hall. 
Fig-. 1. A silicified example ; showing the usual condition of the exterior, and the absence of any defined 
cardinal area. X 2. 
Fig. 3. The interior of a portion of the pedicle-valve ; showing the form of the muscular area. 
Lower Helderberg grouji. Cumberland., Maryland. 
SiTRiFER 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 growth-lines. 
Fig. 8. An enlargement of the cardinal area of the specimen represented in fig. 4; showing the incipient 
develoinnent of the deltidial plates and limitation of the cardinal area. 
Coal Measures. Iowa. 
Spirifer Maia, Billings. 
Figs. 5, 6. Two individuals, showing slight variations in length of hinge and marginal outline. 
Corniferous limestone. Near Columbus, Ohio. 
Spirifer fimbriatus, Conrad. 
See plate 36. 
Fig. 9. An enlargement of a portion of the exterior; shovnng 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. Canandaiqna Lake, N. Y. 
Spirifer lasyis, Hall. 
Fig. 11. A cardinal view of the pedicle-valve ; showing the completed deltidial covering. 
Fig. 12. Extei'ior of a pedicle-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, While and Whitfield. 
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 chambers. X 5. 
Kinderhook group. Illinois. 
Spirifer iiivaricatus, Hall. 
Figs. 1.5-17. 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 Wortlieii). 
Fig. 18. The pedicle-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 group. Crawfcn'dsinlle, Indiana. 
