Still probing the literature to see whether I can match up a protein to the paracrystalline pattern seen in electron micrographs of guinea pig, ferret and sometimes in dog lung, I found a paper which might shed some light on the issue. “Formation of membrane lattice structures and their specific interactions with surfactant protein Nades Palaniyar, Ross A. Ridsdale, Stephen A. Hearn, Fred Possmayer, George Harauz, American Journal of Physiology – Lung Cellular and Molecular Physiology Published 1 April 1999 Vol. 276 no. 4, L642-L649 ” from which I borrowed without permission from the publisher a small portion of one image to compare with a small portion of an image of mine.  Their estimate of the size of the banding pattern at 50 nm in vitro bilayer sheets is very close to my estimate of banding found in vivo, in this case in guinea pig lung, animal M-8041, control, aged, male, I believe.  These are samples from more than 30 years ago, but still represent an enticing visual puzzle.