PLATE 10. 



Raetomya schweinfurthi (Mayer-Eymar). 



FlG. I. Copy of Mayer-Eymar's original figure of the type from the Eocene of Egypt. 

 The remaining figures represent specimens from Southern Nigeria which have 

 been, also, previously published. 



FlG. 2. Left lateral view of a pair of closed valves of medium size. 



FlG. 3. Dorsal view of same specimen showing the depresso-concave anterior end, the 

 laterally approximate umbones, and the posterior gape, enlarged one-fifth. 



FlG. 4. Right lateral aspect of specimen consisting of a pair of valves of larger size 

 than Fig. 2, showing good testiferous structure and the bifurcation of the 

 costae in the central part of the shell. 



FlG. 5. Dorsal portion of an adult example exhibiting the separation of the umbones. 

 Note that the right-hand side of this figure is posterior. 



FlG. 6. Hinge aspect of the smallest example found, representing a left valve with the 

 outwardly projecting chondrophore. 



FlG. 7. A disconnected hinge region of a left valve belonging to a moderately large 

 specimen, showing the triangular chondrophore plate with the long funnel- 

 shaped cavity in front, which is supposed to have held the anterior portion 

 of the resilium. The black bases of Figs. 7 and 8 represent the hard flinty 

 matrix which fills the remainder of the valves. 



FlG. 8. The opposing hinge of same specimen, showing a differently constituted chon- 

 drophore, and which is vertically disposed in the sub-umbonal cavity. 



FIG. 9. The upper surface of an isolated chondrophore plate, showing its coalescent 

 elements, and which must have belonged to a very large example. 



FlG. 10. Basal surface of same specimen, more or less bulbous and furrowed, and quite 

 smooth. 



FlG. II. Portion of a large internal cast with united valves, showing the postero- 

 lateral surface of the left valve with its extensive and rounded pallial sinus. 



