PLATE XXXIII—Continued. 
Fig. 22. An enlargement of the umbonal portion of the bi-achial valve represented in tig. 19; showing the 
structure of the articulating apparatus with more detail, the jiartially closed foramen at the 
apex of the valve, and the low median septum. 
Fig. 23. An enlargement of the surface; a portion of the concentric lamellse showing faint railial striations. 
Oriskany sandstone. Cumherland, Maryland. 
Spirifer arrectus, Hall. 
Fig 24. The exterior of an exfoliated pedicle-valve. 
Fig. 25. The exterioi’ of a large brachial valve, retaining a few of the concentric lamellse. 
Fig. 26. The internal cast of a pedicle-valve ; .showing the cast of the deep muscular impression. 
Fig 27. An enlargement of the external surface. This representation is very imperfect. The exterior of 
the shell is strongly lamellose, each lamella bearing a series of simple spinules. 
Oriskany sandstone. Albany county, N. T. 
