Non-cubic, edge-critical Hamilton laceable bigraphs with 3m edges on 2m vertices

Constructions are given for non-cubic, edge-critical Hamilton laceable bigraphs with 3m edges on 2m vertices for all m ≥ 4. The significance of this result is that it shows the conjectured hard upper bound of 3m edges for edge-critical bigraphs on 2m vertices is populated by both cubic and non-cubic cases for all m. This is unlike the situation for the hard 3m-edge lower bound for edge-stable bigraphs where the bound is populated exclusively by cubics.