Diamond Metallic Bench Plane 1881

I understand that a man named Ellis H. Morris Patent several planes with a diamond shaped base, which was supposed to make the plane move very smoothly. I also understand that Sandusky & Ohio Tools made planes with this base. I believe the Ellis Morris pat. date was in 1871.
Here is my question. When you look at the pictures I've attached on the bottom of this plane their is 1881. I have looked all over the Internet and I can't see what this number 1881 means. I cannot see where Morris had a patent dated 1881. I need someone who really is well versed in planes, to tell me what I have here.