Sentence:  It was a condition of the race, that the horses should be ridden by gentlemen ... [I]t was submitted, that if none were to be reputed in the rank of gentlemen, whose wives had not been visited by Lady Clanricarde, the notion of a <WSD>Corinthian</WSD> Race might as well be given up at once, within twenty miles all round Portumna castle. It would amount, in fact, to a "disgentilizing" of two or three counties. 
Meaning of the word marked with <WSD> tags:  Being a sporting event (originally in horse racing and yachting) restricted to gentleman amateurs.