112 
EXPLANATION OF THE PLATES. 
occur in the Upper Devonian, Petherwin group, Cornwall. The Middle 
Devonian, Torquay group, 8. Devon, and Ilfracombe group, N. Devon. 
Upper Devonian, Baggy and Pilton groups, and Passage beds, Barn- 
staple. Etheridge, Geol. Journ., vol. xxiii., p. 624. In the Carboni- 
ferous rocks it is found in all the stages from the lowest or “ Coomhola 
grits” to the Upper Limestone. In England, Scotland, and Ireland, it 
abounds at many localities. 
