Manhattan Series III Navy - 1
The Series III Manhattan Navy revolvers, like the Series II before them, sported
the December 27, 1859 patent date on the cylinder. A few thousand Series III
pistols probably made in the fall of 1861 would have the scarce
spring plate*
found on serial numbers in the 15000 to 20000 range, and would reappear on
Series IV Manhattan Navy pistols.  The
spring plate can be seen on the Series
III pistol below. It is immediately behind the back of the cylinder.

The photograph also shows a pleasing amount of silver on the trigger guard and
front strap in front of the walnut grip.
* Are you confused about the spring plate? The spring plate was located
between the hammer and the nipples upon which the percussion caps were
placed. The purpose of the
spring plate was to deflect the fire exiting the
nipple laterally and away from the other nipples in order to prevent multiple
ignitions. It also prevented fragments of a spent percussion cap from jamming
the pistol and disabling it.