The mysterious Stone of Mawgan-in-Meneage

I'm on a whistlestop five day trip to Cornwall to conduct some research for a book project I've been writing for the past couple of years. More news on that as it happens.

Today I was out and about on The Lizard peninsula and, passing through the village of Mawgan-in-Meneage, I spotted this stone that I remembered from my youth.

The stone is inscribed but has been so worn by the Cornish weather that it is no longer readable. However, based on an old drawing and a photograph taken in 1936, it could have been a memorial stone to either 'Cnegumus son of Genaius' or 'Genaius son of Cnegumus'. The date of this inscription is not certain beyond having been carved before the twelfth century.

These days, there's a slate plaque at its foot that carries what we believe the inscription says plus a quote that I've not been able to source. 

Any ideas?

A pretty little village too.