Inscription: Marked along the top of the barrel: SMITH & WESSON SPRINGFIELD MASS.
1871.; Marked on top of the cylinder frame: PAT'D APR. 18.1877.; Stamped on the inner face of the cylinder, the serial number: 94421; Stamped on the grip behind the trigger-guard: T over a globe symbol (symbolizing Tiffany's loans to the World's Columbian Exposition); TIFFANY & CO / STERLING / T (for 1891–1902); and a scratched inscription: 5 oz.
What you have is a .32-20 Hand Ejector Model of 1905, and yours is a Second Change revolver (based on the serial number).
However, because it is in the "transition range" of serial numbers, it may be a First Change rather than a Second Change.
Before I could take a stab at giving you an approximate value, I would like to see some good photos of both sides of your gun. Is the missing screw the one that goes up into the front of the trigger guard? Regards, JP JP mentioned the dowel pins on the shell extractor. Does this change the opinion that it is a Second Change Model and if so, how?