First version of the LEGO 2×4 brick, based on Kiddicraft by Hilary Page.
Logo: No logo, no identification marks.
Material: Cellulose acetate (CA).
Slot positions: bslot04 (single slot on the short side) and bslot04a (two slots on opposite short sides).
Inner ribs: On the long side.
Mold numbers: No mold numbers.
Remarkable features: Inner corners rounded.
Colors known: Many colors in many shades, including marbled. White, Red, Yellow and Green seem to be most common.
- It is still unknown if these bricks originated in one single mold, or multiple similar unmarked molds.
[Original post and comments on Flickr]