What renders a book or film compelling depends, obviously, on the reader or viewer. Far more than with the written word, for me a movie, even it is avant garde or speculative, needs to come with a strong narrative backbone. Bear that in mind as I describe “Ammonite,” the new outing for well-regarded filmmaker Francis Lee, as compelling enough scene by scene, but ultimately dreary. Based on the life of Mary Anning, a brilliant but downtrodden fossil hunter in Lyme Regis in the 1840s, Ammonite explores the impact of the arrival of a male fossil expert’s wife to undergo emotional convalescence with Anning, a stay that escalates into lust and love. Kate Winslet and Saoirse Ronan turn in fine performances in the two leading roles, but there are only so many smoldering exchanges and looks one can take while longing for something to happen beyond what is obvious will happen. The bleak, beautiful shoreline is evocatively filmed, the period costumery meticulous, the supporting actors excellent. The trouble is, in my opinion, the script. Given that the core relationship is an act of imagination, one could imagine many ways the plotline could develop, but very little is pursued in Ammonite. My attention was snared throughout, simply because of the sumptuous scenes, but neither character develops much and little drama is evinced. All up, an opportunity missed.