I think it is a Terrier. However I can find no reference to a 4" Terrier...anywhere.






And yes that is a nice fingerprint on the last one.

It looks like it has a square butt, so I think it's a .38 Regulation Police.  Those had 4 inch barrels.  The post-war (post-WWII, that is) guns had a serial number range from 54475 to 122678 and it was produced from 1949 to 1974.  It became the Model 33 in 1957.

This man is correct. What you have is a Pre-Model 33. I can't tell from your pictures if your revolver has the upper side plate screw or not. It is an I-Frame-Improved, which replaced the regular I-frame around 1953. If it has the upper side plate screw, it was made between 53 and 56, if the side plate screw is missing and it doesn't have a model number on the crane, it was made between 56 and 57.