PLATE 54. 
1. 621. 4. Spirifer bilobus. (Pag. 260.) 
1 a, 6. Ventral and dorsal view, where the extremities of the hinge-line are scarcely extended. 
1 c, d. Another specimen, where the extremities of the hinge-line are auriculate. 
1 e. Front view of a specimen, showing the bilobate character. 
1 /, g. Profile views of two specimens, one of which is much more convex than the other. 
1 fc, i. Enlarged figures of a specimen, representing the prevailing form. 
1 fc. Interior of the ventral valve. 
2. 622. 5. Spirifer sulcatus. (Pag.261.) 
2 a. A small specimen, having the cardinal extremities scarcely extended. 
2 6, c. Views of specimens where the cardinal line is extended into mucronate points. 
2 d. An unusually large specimen, having the hinge-line less extended than the preceding. 
2 e. A specimen where the length and breadth are nearly equal. 
2 /. Front view of fig. 2 6. 2 g. Front view of 2 e. 
2 h, i. Profile views of different specimens. 
2 fc. An enlargement of the surface, shoeing the longitudinal striae crossing the lamellae. 
3. 623. 6. Spirifer crispus. (Pag. 262.) 
3 a, 6, c. Ventral views, presenting the ordinary characters of well preserved specimens. 
3 d. An individual, still preserving its natural proportions. 
3 e, /, g. Profile views of three specimens, showing the variable elevation of the beak of the dorsal valve, 
and width of the area. 
3 h, i. Front views of specimens, showing a different proportional convexity. 
3 fc. A portion of the surface enlarged. 
4. 624. 7. Spirifer bicostatus. (Pag. 263.) 
4 a. A dorsal valve of an individual of this species. 
4 6. Ventral view of the same, showing the area and foramen, the beak of the ventral valve being broken off. 
4 c. Profile view, showing the form of the dorsal valve. 
4 d. Front view, in which the elevation of the ventral valve is given as it appears to have been in its perfect 
state. 
4 e. An enlarged portion of the surface, showing the character of the striae. 
5. 625. 8. Spirifer niagarensis. (Pag. 264.) 
5 a, b. Ventral and dorsal views of a young specimen. 5 c. Front view of the same. 
5 d. Profile view of another more gibbous specimen. 
5 e, /, g- Ventral, front and profile views of a well preserved specimen. 
5 fc, i. Ventral and profile views of a well preserved specimen of the ordinary size of this species. 
5 fc. A flattened dorsal valve of about the same size as the preceding specimen. 
5 Z. A flattened ventral valve of a specimen somewhat larger than the preceding. 
5 m. A large specimen, having the form well preserved. 5 n. Front view of the specimen fig 5 h. 
5 o. Cardinal view of a small specimen, where the area is nearly closed. 
bp. Cardinal view of a specimen where the lower part of the shell is compressed. 
5 r. The interior of a dorsal valve, showing the strong lamellae on each side of the triangular foramen. 
5 s. An enlargement of the striae. 
5 t. Section of the plications, showing their form and the number of striae upon the surface. 
6. 452. 3. Spirifer radiatus. (Pag. 265.) 
6 a, b. Ventral and front view of a small specimen. 
6 c. A large specimen entirely flattened, which causes the beak to project as shown in the figure. 
6 d. A specimen from which the shell is partially exfoliated, showing the form of the muscular impression. 
6 e. Cardinal view of the same, showing the entire extent of the dorsal area and foramen. 
6 /. The interior of a dorsal valve, showing the extension of the plates or lam in 33 on each side of the fora¬ 
men, with a central one commencing below the beak. 6 g. Several of the striae enlarged. 
6 h. Transverse section showing comparative elevation and width of striae. 
7. 626. 9. Spirifer pyramidalis. (Pag. 266.) 
7 a. The ventral valve of this species. 7 6. Dorsal valve of the same. 
7 c. Cardinal view, showing the area and long linear foramen which is closed. 
7 d. Profile view of-the same. 
7 e. Several of the plications enlarged, showing the concentric striae. 
