PLATE XXIII. 
(Figures X-18 by R. P. Whitfield.) 
Legend: 
A. 
Cardinal area, pedicle-valve. 
x'. Muscular cavity. 
a'. 
Inner division, pedicle-valve. 
r. Diductor scars. 
a". 
Outer division, pedicle-valve. 
j. Cardinal process. 
F. 
Delthyrium. 
b. Dental sockets. 
s'. 
Apical callosity. 
a. Anterior adductors. 
d. 
x. 
Dental lamellae. 
Pedicle-cavity. 
a'. Posterior adductors. 
Fig. 
1. 
Fig. 
2. 
Fig. 
3. 
Fig. 
4. 
Fig.’ 
5. 
Fig. 
6. 
Fig. 
7. 
Fig. 
8. 
Fig. 
9. 
Fig. 
10. 
Fig. 
11. 
Fig. 
12. 
Fig. 
13. 
Fig. 
14. 
Fig. 
15. 
Fig. 
16. 
Fig. 
17. 
Fig. 
18. 
Genus SPIKIFP^E, Sowerby. 
Page 1. 
Spirifek granulosus, Conrad. 
Dorsal view of a normal adult, retaining the shell. 
The interior of a pedicle-valve ; showing the apical callosity in the delthyrium and the character 
of the muscular area. 
The interior of a brachial valve ; showing the articulating apparatus and muscular area. 
An enlargement of the surface ; showing the papillose character of the shell. 
The central portion of a cast of the brachial valve; showing the striated cardinal process and the 
two pairs of adductor scars. X 2. 
A similar view of another specimen. 
A cast of the muscular area of the pedicle-valve with the muscular impression unusually elongate. 
A similar view of a larger siiecimen. 
Another view of the same, parts, the muscular area being proportionally shorter and smaller than 
in the preceding figure. 
A view of the same characters in another example. All these specimens show variations in the 
form of the muscular area, the size of the adductor scars as well as difierent degrees of devel¬ 
opment of the callosity of the delthyrium. 
A jiortion of the muscular area of the pedicle-valve ; showing its surface markings and the dis¬ 
tinction between the diductor and adductor scars. X 2. 
A profile of an internal cast of the pedicle-valve ; showing the filling of the rostral and muscular 
cavities. 
Similar cast of another pedicle-valve with a more elevated muscular impression. 
An enlargement of a partly exfoliated surface. 
Hamilton shales. Western New Yoi'k. 
An enlargement of a worn surface. The coarse punctations are not structural but probably due 
to some boring sponge. 
Hamilton group. Cumberland, Maryland. 
Spirifer macrothyris, Hall, 
The exterior of a full-grown individual. 
A cardinal view of an imperfect specimen ; showing the elevation of the valves. 
An enlargement of the surface; showing the crenulate margins of the concentric lamellae. 
Corniferous limestone. Near Columbus, Ohio. 
