PLATE XXX. 



(Figures 1-17, 19, 20, m-27, 30 by R. P. Whitfield; 18, 21, 22, 28, 29 by F. B. Meek.) 



Legend : A. Caiilinal area. t. Teelh. 



a'. Iniiei' division. j. Cai'diiial iirocess. 



a". Outer division. b. Dental sockets 



.A. Delthyrium. a. Adductor scars. 



D. Deltidium. r. Diductor scars. 



Genus SPIRIFEK, Sowekby. 



rage 1. 

 Sl'IRIFEK CONCINNUS, Hull. 



Fig. 1. A large individual ; showing the incipient plications on the fold. 

 Fig. 2. Cardinal area of the pedicle-valve retaining the deltidial coveiing. 

 Lower Helderberg group. The Helderbergs, N. Y. 



Spirifer ARENOSUS, Coiu-.id. 

 See Plate 29. 

 Fig. 3. An entire individual, of small size, compared with the New York examples, but near normal pro- 

 portions for this locality. 



Oriskany sandstone. Cumherland, Maryland, 

 Fig. 4. The internal cast of a jiedicle-valve ; showing the great diductor scars, enclosing the adductors. 

 Fig. 5. The central cardinal portion of an internal cast of the brachial valve; showing the form of the 



cardinal process and the size of the adductor seal's. X 1^- 

 Fig. f). The ai'ticulating apparatus of the brachial valve. 



Fig. 7. The cardinal area of a pedicle-valve j showing the deltidial covering and teeth 

 Oi-iskany sandstone. Eastern New York. 



Spirifer unicus, Hall ( = S. arenosus, Coiujid). 



Fig. 8. The original specimen ; showing the plicated sinus. 



Upper Helderberg group. Clarence Hollow, N. ¥. 



Spirifer Grieri, Hall. 



Figs. 0-11. Views of a normal individual. 



Fig. 12. The brachial valve of a larger shell with stronger plications on the fold. 



Fig. 13. Front view of the same .specimen. 



Upper Helderberg group. Oliio. 



Spirifer disjunctus, Soweiliy. 



Fig. 14. The internal cast of a pedicle-valve with alate cardinal extremities ; showing the size and composi- 

 tion of the muscular area. 



Chemung group. Meadville, Penn. 

 Fig. 15. A small, nearly entire individual, retaining the shell. 

 Fig. 17. The internal cast of a small, short-winged pedicle-valve. 



Sandstones of the Chemung group. Western New York. 



Spirifer disjunctus, Sowei-by, var. sulcifer, var. iiov. 



Fig. 16. The internal cast of a brachial valve ; showing the sulcus on the plicated median fold. 

 Chemung group. Near Olean, N. Y. 



Spirifer Whitneyi, Hall. 



Fig. 18. An individual of normal size, but rather short hinge. 

 Fig. 19. The interior of a brachial valve. 



Chemung group. Rockford, Iowa. 



