A quick Google search yielded the following from the Wikifaqs Website (www.wikifaqs.com):
"What is the age and value of a J Stevens Arms and Co Model 235 shotgun?
Answer:
The model 235 was manufactured from 1912 to 1932 (no Stevens guns were made from 1916 to 1920). Value will range from $50 if beat-up and rusted to $300 if like-new and never fired. Most will trade for around $200."
If you hope to use this gun I strongly recommend having it checked out first by a competent gunsmith. Have him/her pay particular attention to the barrels: no bulges, dents, excessive corrosion, crystalized solder, or thin spots throughout their length. If they prove to be sound, then you can have the smith proceed with cleaning, etc.