Depends on the model, and condition. Model number should be under the receiver, or on the top tang, unless it is a model 1898, which had no markings to indicate model.
The Marlin model 24 shotgun was produced by Marlin from 1908-1915.
To determine exact value of a 1904 Marlin 12 gauge pump shotgun, you would actually have to take a number of factors into consideration. The main thing to consider would be the condition of the shotgun.
in good shape they sell for about$300 to $500,open hammer pump shotgun
50-250 usd
Anywhere from 200 to 500 depending on condition
$1,000,000.00
Model 49, 3000 made form 1925 to 1928 only
The Model 49 was a variant of the basic Marlin pump shotgun produced on the 1889 patents. The Model 49 was made in the late 1920's and was primarily an incentive gift for stock purchasers. Due to several different potential problems with the action, Marlin advised owners of these guns not to shoot them.
If it shoots, $75-$450 depending on condition.
it is a 410 ga pump shotgun
If your pump 12 ga. has an exposed hammer, it's most likely a model 1898, as all later models of exposed hammer Marlin shotguns had the model marked on the upper tang behind the trigger. If it is not an exposed hammer, then the model designation is on the bottom, where the receiver meets the mag tube.
Marlin Model 49 Exposed Hammer Pump Shotgun, 3000 made 1925-1928 for stock purchasers only, 12 gauge 2 3/4" with 30" barrel, 4 round magazine