PLATE 27. 
Legend: D, Deltarium. A Delthyrium, 
A. Cardinal area. Dg. Deltidial grooves. 
a’. Its inner division. s'. Rostral callous. 
a". Its outer division. Adt. Denticulations. 
t. Teeth. r. Diductors. 
SPIRIFER, Hau. 
(APERTURATI.) 
Page 756. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
SPIRIFER IMBREX, Hall. 
. The exterior of a brachial valve. 
Burlington limestone. Burlington, Iowa. 
SPIRIFER suB&ZQuALIS, Hall. 
. Dorsal view of the original specimen. 
Warsaw limestone. Warsaw, Illinois. 
SprrirFerR Marronensis, Shumard. 
. Dorsal view of a rather small example; showing the fasciculate 
plications. , 
Choteau limestone. Pike county, Missouri. 
SPIRIFER concrnnus, Hall. 
. Dorsal view of a large individual; showing the incipient plications on 
the fold. 
. Cardinal area of the pedicle-valve retaining the deltarium. 
Lower Helderberg group. The Helderbergs, N. Y. 
Sprrirvek GRieRt, Hall. 
. Dorsal view of a normal example. 
Upper Helderberg group. Ohio. 
Spreirer Orestes, Hall and Whitfield. 
. A normal adult individual. 
Chemung group. Rockford, Iowa. 
SPIRIFER INCREBESCENS, Hall. 
. A rather small example with extended hinge-line. 
. A portion of the interior pedicle-valve; showing the denticulations 
along the hinge-line, the delthyrial callous and the form of the 
muscular scar; enlarged. 
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