The 1951 Pictorial series of Dominica is a popular hunting ground for some extremely rare watermark varieties which occur on just the horizontal designs; namely "A" of "CA" missing, "C" of "CA" missing, or "JA" for "CA". This was caused when the letters on the dandy roll that is impressed into the paper pulp, accidentally fell away. The "JA" error is presumably a poor attempt at a repair job.
This example clearly shows the "C" completely missing on the top possible value ($1.20) from the set. It is also in very fine mint condition.