Welcome to the Forum. The proper name for this revolver is a 38 Single Action, 1st Model. There were a total of 25,548 made in those two years. There was a 38 Single Action, 2nd Model made with several improvements from 1877 to 1891 and that production totaled 108,255.
The caliber was 38 S&W which is still manufactured today. Those Mother-of-Pearl stocks are not original to the revolver, being been first available some 20 years later than your gun was made. The early guns had were black hard rubber with a block lettered S&W in the top round.
Value is not big money. Without the original stocks, in decent condition with most of the nickel remaining, maybe $400. The MOP stocks have one chip in them, but should sell for $125 or more. Problem is the original stocks are hard to find and may be worth more than the MOPs you have.