PLATE XX. 



Figs. 1, 2, 3, and 7. — Naiadites crassa. A series of valves showing the striated 

 hinge-plate, and almost obsolete cardinal tooth and pit-like muscle-scars. From 

 the Cults Lime Works, Pitlessie, Fife. My Collection. (Page 147.) 



Fig. 4. — Naiadites crassa. A specimen with the valves united, but slightly 

 displaced. Same locality. My Collection. (Page 147.) 



Fig. 5. — Naiadites crassa. A dwarf variety. From the Wardie Shales, Wood- 

 hall, Water of Leith. My Collection. (Page 147.) 



Fig. 6. — Naiadites crassa. External view of fig. 5. 



Fig. 8. — Naiadites crassa. The worn surface of a left valve. From Cults, 

 Pitlessie, Fife. My Collection. (Page 147.) 



Fig. 9. — Naiadites crassa. A specimen exhibiting both valves spread open. 

 From the Carboniferous-Limestone Series, Beith, Ayrshire. In the Collection of 

 Mr. J. Neilson, of Glasgow. (Page 147.) 



Fig. 10. — Naiadites crassa. A cast showing mantle-line and muscle-scars. 

 From the same locality and Collection. (Page 147.) 



Fig. 11. — Naiadites crassa. A fairly perfect right valve, showing dimensions. 

 From Cults Lime Works, Fife. My Collection. (Page 147.) 



Fig. 12. — Carbonicola elegans. A cast showing muscle-scars. From the Calci- 

 ferous-Sandstone Series, East of Pittenweem. (Page 81.) 



Figs. 13 and 15. — Carbonicola elegans. A right and a left valve. From the 

 same locality. (Page 81.) 



Fig. 15 a. — Carbonicola elegans. A line to show the vertical curvature of the 

 valve. (Page 81.) 



Fig. 11. — Carbonicola elegans. The hinge enlarged to twice its size. From the 

 same locality. (Page 81.) 



