As an example of dogtooth Ruskin gives:
He seems consistently to use the word in that way, though that form would now be defined as ‘nail-head’. It is found in Romanesque and early Gothic building, and in England is found in buildings categorised as Norman or Transitional.
Ruskin appears also to use the word ‘dogtooth’ as it is used now of the slightly later form, found in Early English Gothic:
made up of four lobes radiating from a raised central point. At Works, 10.280 he appears to suggest that the two words, nailhead and dogtooth, are synonymous.
[Version 0.05: May 2008]