As early as the mid-1930’s Leitz Wetzlar offered lens containers composed of material generally known as Bakelite. Prepared for individual focal lengths, the cases feature a screw on cap and exhibit at least two colors (black or brown). Occasionally the black case has a very subtle reddish tinge.
The cases are fragile and many have cracked, chipped or totally disintegrated after decades of service. Handle them carefully. Share your case with LHSA especially if different than the units illustrated.