Hi JTB - the ones you attached above are definitely in the Apple 3DMF format.

When trying to open them in Rhino, Rhino reports "AR0020A.3DM is not a Rhino file", and if you open them in notepad you'll see that they are text files where the first few lines read:

3DMetafile

#
# QuickDraw 3D file: D:\ARecon3d1\3Dmf\ar0020a.3dm
#

- Michael