PLATE XLII. 
(Figures 1-6,11-21, 25, 27-29 by E, Emmons; 7-10, 22-24, 26, 30-32 by R. P. Whitfield.) 
Legend: 
pi. Shoe-lifter.” 
t. Teeth. 
dl. Dental lamellae, 
hp. Hinge-plate, 
s. Septum of brachial valve. 
b. Dental sockets. 
c. Crura. 
a. Adductor scars, 
r. Diductor scars. 
Genus MERISTA, Suess. 
Page 70. 
Merista Tennesseensis, sp. IIOV. 
Figs. 1, 2. Two views of the exterior of a somewhat elongate example. 
Fig. 3. The interior of a pedicle-valve of a broader form ; showing the “ shoe-lifter ” process. 
Fig. 4. The interior of a brachial valve of the same specimen ; showing the divided hinge-plate and the 
median septum. 
Fig. 5. The exterior of the pedicle-valve ; showing the cavity left by the removal of the “ shoe-lifter.” 
Fig. 6. A broad individual viewed from the brachial valve. 
Lower Helderberg group. Perry county, Tennessee. 
Merista typa, Hall. 
Fig. 7. The interior of a pedicle-valve somewhat incomplete about the margins ; showing the great width 
of the “shoe-lifter,” and the extension of the dental plates uiion its surface. 
Figs. 8, 10. Two views of the exterior of a normal adult specimen. 
Fig. 9. Interior of a pedicle-valve in which the “ shoe-lifter” is highly arched and the dental lamellse con¬ 
spicuously thickened. 
Fig. 11. A pedicle-valve having a very broad and low “ shoe-lifter,” and short, scarcely divergent dental 
plates. 
Fig. 12. An imperfect pedicle-valve with sharply angled and highly elevated “ shoe-lifter,” and prominent 
dental plates. 
Lower Helderberg group. Cumberland, Maryland. 
Subgenus DICAMARA, s.-gen. nov. 
Page 73. 
Dicamara scalprum, F. Roeiiier. 
Fig. 13. A profile of a specimen cut to show the form of one of the spiral cones. 
Fig. 14. View of the same preparation from the pedicle-valve ; showing the spirals and the cavity left by 
the removal of the “shoe-lifter.” 
Middle Devonian. Hartz Mountains {?), Germany. 
Fig. 15. The interior of a brachial valve; showing the “ shoe-lifter,” and the dividing median septum. 
Drawn from a gutta-percha impression which retains on the posterior margin a portion of the 
pedicle-valve. 
Fig. 16. A view of a specimen which shows the cavity left by the removal of the “ shoe-lifter ” of the bra¬ 
chial valve, the median septum remaining in place. The apical portion of the cavity of the 
“ shoe-lifter ” of the pedicle-valve is also shown. 
Middle Devonian. Pehn, Germany. 
