PLATE 43. 



Page 



Pijis. 1-8. Spirifera alta 248 



1-3. Caste of dorsal valves, showing the extent of area, dental cavities, and muscular impres- 

 sion. 



4, 5. Two views of a cast of a ventral valve, showing the muscular impression and sinuate out- 

 line of the valve in front. 



•, 8. Cardinal views of a ventral valve taken from gutta-percha casts, from natural moulds, 

 showing a partial closing of the triangular foramen by shelly matter, which is not the 

 true deltidial plate. 



7. Cardinal view of a cast of a ventral valve, showing the cavities left by the removal of the den- 

 tal lamellse, and the concave impression of the inner surface of the shelly plate, which 

 pailially closed the foramen. 



