PLATE XLIV. 



(Figures 1-12, 15-19, 23, 24, 27, 28, 31, 32 by E. Emmons; 13, U, 20-22, 25, 26, 29, 30 by R. P. Whitfield.) 



Legend : ilp. Deltidial plates. r. Didiictor sears. 



p. Pedicle-cavity. a. Anterior adductors, 



d. Teeth. a'. Posterior adductors. 



Genus MERISTELLA, Hall. 



Page 73. 



MeRISTELLA BELLA, Hall. 



See Plate 43. 



Fig. 1. The intenor of a pedicle-valve ; showing the teeth, the deeply excavated muscular area and the 



testaceous thickening which fills the pedicle-cavity except along the median line. 

 Fig. 2. The interior of the lirachial valve ; showing the suliquadrate outline of the hinge-plate, its 



post-lateral expansions and the ante-lateral position of the crural bases. X 3. 

 Fig. 3. The hinge-plate viewed in profile from the anterior margin of the brachial valve ; showing its con- 

 cave surface, the elevation of the crural bases and the median supporting septum. 

 Lower Helderberg group. The Helderbergs, N. Y. 



MkRLSTELLA LyEVIS, Hill]. 

 See Plate 43. 

 Fig. 4. The hinge-plate ; showing its subtriangular form, median concavity and supporting septum. X 3. 

 Lower Helderberg group. Albany county, N. Y. 



Meristella arcuata, Hall. 



See Plate 43. 

 Fig. 5. The hinge-plate viewed from in front ; showing the dental sockets and socket-walls, elevation of 

 the crural bases and the median septum. 



Lower Helderberg group. Schoharie, N. Y. 



Meristella Walcotti, sp. iiov. 



See Plate 43. 



Fig. 6. The spirals and loop, naturally preserved by incrustation of silica, and exposed by the removal 

 of the pedicle-valve. The specimen is viewed from the anterior margin, and in the cavity be- 

 tween the cones is seen the looji with its scissors-shaped branches. 



Fig. 7. The same specimen viewed from the posterior margin, and showing the position of the branches 

 of the loop with reference to the ribbon of the spiral cones. 



Fig. 8. A similar preparation, to which a portion of the internal cast of the valves adheres. The speci- 

 men 13 viewed from the dorsal side and shows the form of the spiral cones and the length of the 

 median septum. 



Fig. 9. An internal longitudinal view ; showing the 'position and form of the loop and one of the .si)iral 

 cones. Partially restored. 



Fig. 10. A naturally incrusted brachidium viewed from the dorsal side, and showing the prominence of 

 the primary lamellte of the cones. 



Fig. 11. A similar specimen ; showing the spiral cones on tlie ventral side. 



Fig. 23. A view of the brachidium from the ventral side, a portion of the cones being omitted to show the 

 primary lamellae and loop. Restored. 



Fig. 32. The hinge-plate. Drawn from a gutta-percha cast. 

 Oriskany sandstone. Cayuga, Ontario. 



Meristella lata, Hall. 



Fig. 12. An internal cast of the pedicle-valve ; showing the filling of the pedicle-cavity and of the deep 

 muscular impression. 



Oriskany sandstone. Albany county, N. Y. 



