i6, 17 More or less exfoliated parts of the surface, x 5 



18 Internal cast of a veutral valve 



19 Similar view with spines retained 

 20, 2 1 Ventral valves 



22 Interior of a large ventral valve, part of the shell being lost 



23 Exterior of a ventral valve 



24 Internal cast of a large ventral \-alve 



Gaspd sandstone. Gaspe Basin 



345 



