PLATE XLII. 



(Figures 1-6, 11-Jl, 25, JT-'-'O by K. Emmons; 7-10, 2i-24, 26, 30-32 by K. P. Wuitfiei.d.) 



Legend: pi. "Shoe-lifter." b. Dental sockets. 



t. Teeth. c. Crura, 



dl. Dental laniellie. a. Adductor scare, 



hp. Hinge-plate. r. Diductor scars. 

 a. Septum of brachial valve. 



Genus MEKLSTA, Suess. 



I'iigc 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 divide<l 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 emmty, 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 upon its siii'face. 

 Figs. 8, 10. Two views of the exterior of a noi'mal adult specim-rn. 

 Fig. 9. Interior of a pedicle- valve in which the " shoe-lifter " is highly arched and the dental lamella; ccm- 



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 grouj). Cumberland, Maryland. 



Subgenus DIG AM AR A, s.-gen. nov. 



Page 73. 



DiCAMARA scalprum, F. Rociiicr. 



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 Dr-vonian. Hartz Mountains {?), Oermany. 



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. Pelm, Oermany. 



