168 
crystallized Carbonate of Iron or Carbonate of Lime, adds 
to its variety and beauty. The same species of shell is dis- 
covered at other places under different circumstances. My 
good friend, James Brodie, Esq. brought me specimens 
from Craymouth in a more granular marly Limestone, in 
which nearly the whole of the shelly part is more or less 
replaced by a brown sparry crystallization exactly forming 
the contour of the shell. They are also found loose and 
very perfect, and sometimes in small masses or separate, 
cast in Pyrites, as at Exmouth. There are seldom other 
shells in this congeries besides the one now described, and 
a keeled Ammonite generally of a larger size and sufficiently 
characterized to form another Genus perhaps, hereafter to 
be noticed. 
