Treadwell Primer

I have heard of a Treadwell Primer in connection with Frankford Arsenal c1870. What does it look like?

From Berkeley Lewis’ Smithsonian publication book on Small Arms Ammunition at the International Exposition Philadelphia, 1876

318 Copper disk anvil in reinforcing cup, both
held by two large stab crimps .125 from
base. One of Col. Treadwell’s experiments
with gas checks. The head has a .125 hole
to increase sensitivity over the primer area.
C-1.750. [Figure 43.]

349 Treadwell cube anvil; brass case, reinforced
with inside ring. Pocketed for outside cap
containing a cubical anvil. Plain flat head.
Frankford, 1872. C-1.767, R-.667, H-.565,

351 Treadwell spherical anvil. Case reinforced
with solder in flange. Pocketed for outside
cap and spherical anvil. Frankford, 1872.
Same as last two and

374 Treadwell open base, double cup, as made
for .45 caliber. Brass case. Copper cup anvil
inside long reinforcing cup, held by two
crimps .250 from base. Hole through base
.146 inch. Frankford, 1873. [Figure 73.]