DizLasMA, sp. ? 
Fig. 18. Cardinal view of a specimen enlarged to show the oblique opening of 
the pedicle-passage and its cross-striated surface. x 3. 
Fig. 14. An internal cast of a brachial valve; showing the form of the muscular 
platform. x 3. 
Chester limestone. Caldwell county, Kentucky. 
DretasMaA FormosA, Hall. 
Fig. 15. Dorsal view of a specimen, cut to expose the loop. 
Figs. 16, 17. Dorsal and profile views of a characteristic and somewhat gibbous 
example. 
St. Louis group. Washington county, Indiana. 
Fig. 18. A cast of the cardinal portion of the pedicle-valve, enlarged to show 
the cavity left by the enfolded margin of the pedicle-passage, the 
dental lamellz and deltaria. 2. 
Fig. 19. An internal cast of the brachial valve; showing the impression of the 
muscular platform and the genital markings. 
St. Louis group. Washington county, Indiana. 
Dietasma Rowtey1, Worthen. 
Fig. 20. Dorsal view of an internal cast; showing the impression of the 
muscular platform of the brachial valve. 
Choteau limestone. Graydon Springs, Missouri. 
Dre_asmMA BovipENs, Morton. 
Figs 21, 22, 23. Dorsal, profile and ventral views of a large and characteristic 
example; showing the curvature of the valves and the oblique for- 
aminal aperture. 
Carboniferous limestone. Harrison county, Missouri. 
Fig. 24. Dorsal view of an internal cast of a narrow shell, in which the impres- 
sion of the muscular platform of the brachial valve is sharply 
defined. 
Fig. 25. The reverse of the upper portion of the same specimen; showing the 
introverted lamella about the foramen, a portion of the dental plates 
and the form of the muscular platform. 
Carboniferous limestone. Locality ? 
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