That is not a Crass. The Crass Model was the first hammerless Ithaca. That is an NIG (New Ithaca Gun), the hammer model, which in 1887, replaced the original Baker Model hammer gun Ithaca built. The NIG was built and serial numbered concurrantly with the Crass, Lewis, Minier and Flues Model hammerless Ithaca doubles up to 1915 when Ithaca introduced their short lived "two-bolt" Model hammer gun, sort of a hammer version of the Flues. Here is the same grade from 1910 --
after they removed the reinforcing bolsters from the sides of the frame.