DESCRIPTION* OF 



PLATE IV. 



Page 



Fig. 1. SPIRIFER HUNGERFORDI. 501 



1 a, b. Dorsal views of two individuals, showing the form of shell, portion 



of area, etc. 



1 c, d. Ventral views of two individuals. 

 1 e. Profile view of 1 b. 



If. Front view, the ventral valve being ahove. 

 1 g, h. Dorsal and profile views of an old shell. 

 1 t. Ventral view where the shell has been ground off to show the internal 



spires. 



1 fc. Interior of the ventral valve, showing the foramen and dental lamellae 



which extend downwards to the middle of the shell. 



Fig. 2. SPIRIFER WHITNEYI. 502 



2 a, b. Ventral and dorsal views of a specimen of medium size. 

 2 c. Cardinal view of the same. 



2 e. Enlargement, showing the fine striate and granulose surface. 



Fig. 3. SPIRIFER SUBMUCRONATUS, read SUBATTENFATUS. 504 



3 a, b. Dorsal and ventral valves of a specimen having one hinge extremity 



produced more than the other. 



3 c. Cardinal view of the same specimen. 



Fig. 4. SPIRIFER INUTILIS. 505 



4 a. View of the ventral valve. 



4 b. Cardinal view, showing the area and foramen. 



4 c. Enlargement of the surface of fig. 4 a. 



Fig. 5. SPIRIFER FIMBRIATUS. 505 



5 a. Fragment of a ventral valve in which the sinus is subangular. 



5 b. Cardinal view of the same, showing the broad foramen which occupies 



a large part of the area. 



5 c. Dorsal valve of a small individual preserving the spiniferous bases. 

 5 d. Profile view of a small specimen from the Hamilton group of >'ew-York. 



5 e. Enlargement of the surface as it usually appears when the bases of 



the spines are preserved. 



Fig. 6. SPIRIFER BIMESIALIS. 507 



6 b. Dorsal valve of an apparently full-grown specimen. 



6 c. Cardinal view, showing the area, foramen and part of the dorsal valve. 



6 d. Ventral valve of another specimen, showing the small plication in the 



centre of the mesial sinus. 



Fig. 7. SPIRIFER ASPERA. 508 



7 a. Ventral valve of a specimen less than the full size. 



7 b. Cardinal view of the same, showing the area and foramen which is 

 partially filled with the pseudodeltidium . 



7 c. Dorsal valve of a large individual which shows about twenty plica- 

 tions on each side of the mesial fold. 



7 d. Enlargement of the surface, showing the granulose character with a 



few distinct imbricating lines. 



Fig, 8. SPIRIFER PARRTANUS. 509 



8 a. Dorsal view, showing the beak of the ventral valve, the area in part 



with the foramen, etc. 

 8 b. Ventral valve of the same specimen. 



