This horn coral fossil appears to be a Duncanella sp. It was found in the Waldron Shale of Indiana. The fossil dates to the Silurian Period (425-419 million years ago).
My experience while collecting in the Waldron Shale that there are maybe 2-3 varieties of horn corals found there. The one in this posting is more elongated and not so stubby like the other variety found. I used this web page to identify the fossil.