The answer to your question is that it is supposed to be a Lion's Head erased and it is the crest of the arms of Earle (with an 'e' on the end) of Swallowfield Place, Berkshire. The arms themselves are blazoned 'Gules three Escallops a Bordure engrailed Argent'.

It doesn't even look anything like a horse's head! The crest given in the other answer (the Nag's Head) does not go with the shield that you have shown in your image.

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I have done most of the research about the crest myself but the crest above the plate helm i am stuck on.
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What research have you done?