118 
THE GEOLOGIST. 
ternal layer of bone, either in the regularity of the "wave or in the grace 
of the curve of the ridgqs. It may be otherwise in the English Pteras- 
pides, but no Scottish specimen, which I have seen, presents us with the 
cornua so fully developed in the kindred Cephalaspis. 
I may add that I have had no further light thrown on the nature of the 
protection of the under side of the head of Pteraspis. I can only see, from 
the specimens I possess, that the plate of the upper side has a broad mar- 
ginal rim or border turning downwards or inwards, but whether to lock into 
another plate I cannot affirm. Hugh Mitchell. 
Craig, Fehniary 13, 1864. 
Flint Implements. — Sir Charles Lyell says, in his * Antiquity of Man,* 
that flint-implements have occasionally been found on the beach between 
Heme Bay and the Reculvers, and that they are somewhat rare, since, so 
far as is known, not more than about twelve have been met with there. 
The most recent find is, I think, in my possession. In August, 1863, 1 spent 
some little time in attempting to discover the formation from whence these 
flints are derived, by, if possible, finding one in situ; failing in that, I de- 
termined to search the beach, and there saw one lying on its flat side on 
