PLATE 23. 
Legend: D. Deltidial plates (deltarium), b. Dental sockets. 
t. Teeth. x. Extension of crural plates. 
d. Dental lamellee, a. Adductors. 
s. Med? .n septum. r. Diductors. 
ce. Crura. j. Cardinal process. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
ci) 
SPIRIFER, Sowerry. 
(Rap1art1.) 
Page 753. 
SPIRIFER RADIATUS, Sowerby. 
. Dorsal view of a specimen retaining the deltarium and external surface. 
. The interior of a pedicle-valve; showing the teeth and muscular 
impressions. 
. A portion of the interior of the brachial valve; showing dental sockets 
and crural plates. 
Niagara group. Waldron, Indiana. 
. The interior of a portion of conjoined valves; showing a low median 
septum in the brachial valve. 
Niagara dolomites. Wisconsin. 
Sprrirerk Evupora, Hall. 
. The exterior of the pedicle-valve; showing the lineate surface. 
. An enlargement of the surface. 
Niagara group. Waldron, Indiana. 
SPrRIFER PLICATELLUS, Linné. 
. Dorsal view of a typical specimen from the upper Silurian of Sweden. 
SPIRIFER MACROPLEURA, Conrad. 
. A dorsal view of a normal mature individual; showing the external 
characters. 
. An internal cast of the pedicle-valve; showing the impressions of the 
pedicle-, adductor and diductor scars. 
Lower Helderberg group. The Helderbergs, N. Y. 
198 
