These are 55-ton two-bay, open top hoppers. They had their ends extended, called "peaked ends" (a.k.a. "heap shields"), to help them carry even more of a load. Additionally, their bottoms were extended downward, called "fishbelly", to also extend their load capacity. These cars were a progression in the design from the basic 50-ton two-bay hopper. These cars saw service starting in 1937.
(external link: N&W Historical Society)