PLATE 28. 



Page 



Fig. \ a-f. Spirifee modesttjs. 203 



1 o. Dorsal view of a specimen of ordinary size. 

 1 J, c, d. "Ventral, dorsal and profile views of a larger individual. 



1 e. The interior of the ventral valve. 

 1/. Front view of 1 a. 



Fig. 2 a-/. Spirifer sAFFORDi. 203 



2 a, 6, c. Dorsal, ventral, and profile views of the same specimen. 



2 c. Front view of the same. 

 2/. Enlargement of the surface. 



Fig. Z a - d- Spirifer tenuistriatus. 204 



3 a, b, c. Ventral, dorsal, and profile views. 

 3 d. Enlargement of the surface striae. 



Fig. i a - e. Spirifer octocostatus. 205 



4 a, b, c. Ventral, dorsal, and profile views. 



^ a \,b \, c \. Ventral, dorsal, and profile views of other specimens. 



4 d. Cardinal view of 4 c t, showing the foramen. 



4 c. Interior of the ventral valve. 



Fig. 7. Spirifer concinnus. 200 



7 a, b. Dorsal and ventral views of a large specimen from the Upper Pentamerus limestone. 



Fig. % a - d. Spirifer macropleurus. 202 



8 o, 6, c. Casts of the ventral valve, showing some variety in the forms of the muscular im- 

 pressions. 



8 d. Enlargement of the surface stria;, taken from an impression of the exterior in the shaly 

 limestone where the shell has decomposed. The concentric striae are rarely preserved on 

 the surface of the shell. 



