Owner Comments:
JNDA 01-13A. Dragon obverse and sun reverse motifs.
In 1871 the Japanese Mint reduced the diameter of the 50 sen coin by a fraction of a millimeter, while the weight remained the same, presumably for either technical or planchet acquisition purposes.
There are two varieties for the 'small diameter' version. The significantly more difficult one is the 21 mm beaded circle version. Other than measuring the circle, one of the flames (at approximately 2 o'clock) is seen overlapping 2 of the dragon's spines. There are also other variances with regard to the limb spines as well, but the diameter and the flame are the most common descriptors.
It can be confusing vs. the larger diameter dragon coin (the 1870-1871 31.51 mm coin) as that one also appears to overlap two spines. However, in the absence of good calipers, there are even more pronounced differences in the limb spines to differentiate.
31.0 mm in diameter, 0.800 fine silver, weight 12.5 grams.