PLATE XLII. 



(Figures 1-6, ll-«, 2S, 27-29 by E. EHHONs; 7-10, 22-24, 26, 30-32 by R. P. Whitfield.) 



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



t. Teeth. c. Crura, 



dl. Dental lamellae. a. Adductor scare. 



hp. Hinge-plate. r. Diductor scare, 

 s. Septum of brachial valve. 



Gknus MERISTA, Suess. 



Page 70. 



Merista Tennesseensis, sp. nov. 



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 j 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 tyfa, 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 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 lamellffi 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. RoGiiier. 



Kg. 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 i-emoval of the " shoe-lifter." 



Middle Devonian. Hartz Mountains (?), Germany. 



Fig. 15. The interior of a brachial valve j 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, Germany. 



