Explanation of Plate XXII. 



The views on this plate are natural size and are taken from brachiopods 

 belonging to a species of Productus occurring commonly in the Lower Knob- 

 stone shales of Kentucky. 



Figs. 1 and 2. Dorsal and ventral views of a rather large specimen which 



has been only slightly fractured. The two valves of this species 



are less than one-eighth of an inch in thickness. 

 3 and 4. Opposite views of another shale specimen, which, however, has 



suffered crushing as well as fracturing of the shell. 

 5 and G. Dorsal and ventral sides of an example from a water zone. The 



interior and the main fracture lines at more or less right angles to 



the beak have been filled with silica so that the thickness of the 



shell is almost equal to the length. 

 7 and 8. Two examples still further enlarged by silica. 

 9 and 10. A geode with a Productus as its basis. In tig. 9 the dorsal 



valve of the shell is seen while the view in fig. 10 shows the edge 



of both valves. 

 150 



