PLATE XXXIV—Continuea . 
Fig-. 21. An enlargement of tlie external lamellose surface. 
Hamilton group. Western New York. 
Fig. 22. An internal cast of a pedicle-valve with gi'eatly extended and attenuate cardinal extremities. This 
and approximate forms are very abundant in the coarser shales of Albany, Schoharie and 
Otsego counties. 
Hamilton group (sandy shales). Schoharie county, N. Y. 
Spirifer bimesialis, Hall. 
Fig. 23. A cardinal view of conjoined valves ; showing the height and slight incurvature of the area. 
Fig. 24. The exterior of a brachial valve. 
Fig. 25. The exterior of a specimen more extended on the hinge. 
Fig. 26. An enlargement of the external surface ; showing the imbricating lamellEe. 
Upper Devonian. Independence, Iowa. 
Spirifer mucronatus, Conrad, var. posterus, var. nov. 
(This shell in one of its forms was identified as Delthyris mucronata, in Geology of New York ; 
Report on the Fourth District, 1843 (p. 270, fig. 3), and the shell termed in that work D. acuminata. 
Hall, is probably the same form. It is a vai-iation from the typical form of S. mucronatus, 
similai- to tho.se represented in figs. 15 and 16 of this plate, with broad or narrow bodies and 
acuminate cardinal extremities. The original term, acuminata, can not be applied to this shell 
on account of preoccupancy.) 
Fig. 27. The exterior of a brachial valve ; showing the lamellose surface and extended cardinal extremities. 
Fig. 28. An internal cast of the pedicle-valve; showing the impression of the muscular area but no evi" 
dence of the median septum which exists in S. mesacostalis. 
Figs. 29, 30. Internal casts of brachial valves. 
Fig. 31. The centi'al portion of an interior of the brachial valve, enlarged ; showing the muscular scars 
and articulating apparatus. 
Chemung group. Tompkins county, N. Y. 
Spirifer mesacostalis, Hall. 
Fig. 32. View of the exterior of an extended specimen ; showing the lamellose surface and biplicate 
median fold. 
Fig. 33. 4 pedicle-valve ; showing the plication in the median sinus. 
Chemung group. Allegany county, N. Y. 
Fig. 34. A cardinal view of conjoined valves ; showing the width of the cardinal areas. 
The smaller and shorter forms of this species diffei’ little in general aspect from Sp. mucronatus in 
some of its varieties, and in its squamose surface, but the cardinal area is distinctly wider, the 
median fold deeply duplicate and an angular plication in the median sinus. The casts of the 
interior are readily distinguished by the presence of a distinct septum in the ventral valve. 
