The Chaucer Review: An Indexed Bibliography (Vols. 1-30)

Finlayson, John. "The Form of the Middle English Lay." 19 (1985): 352-68.
Few Middle English texts can claim to be lays, works modelled on the Breton lays of Marie de France. Generally, lays are "set in Brittany, concern love, and have a functional magical element" (361), though lays vary substantially between themselves. The similarities between Sir Degare, Le Freine, and Sir Orfeo, particularly in word choice may result from a joint author-translator. Examination of the works claiming to be lays--the Franklin's Tale, Erl of Tolous, Sir Launfal, Emaré, and Sir Gowther--shows that they can be divided into two types, but that the later works modify the form of the lay considerably.

Yoder, Emily K. "Chaucer and the 'Breton' Lay." 12 (1977): 74-77.
The term "Breton" lay as used by Chaucer and the writer of Sir Orpheo refers to rhymed narrative produced in Britain that is, the British island, not Brittany in what is now France, before the Germanic invasions or, after the invasions, in pockets held by the Celts and the Welsh.