"he wrote in terza riruce which endeared him to Ezra"

It is thought Hemingway meant that Dunning wrote in the poetic form known as 'terza rima', rather than 'terza riruce', which may have been a mistake on the part of the typist or editor charged with handling the hand-written manuscript.

Terza rima is a form of poetic stanza based on a particular three-line system of rhyming.