This newspaper advertisement is at www.thepotteries.org. It is from an ad in The Pottery Gazette, February 2, 1880. The trademark noted in the ad is the same one on the shard found on Eastport's shoreline.
Books.google.com: A Book of Pottery Marks by W. Percival Jervis, 1897; Pg 10 of the older book. Note that when you read the books.google the page numbers change when you read in their format, and if you download.
"In 1832 the present business was started by REED & CLEMENTSON; Jos. Clementson shortly after becoming the sole proprietor. In 1856 he purchased the BELL WORKS, formerly operated by Wm. Ridgway, whom retired in 1867 and died in 1871. His four sons continued the business."
This shard is different from the one sketched in the above book by Percival Jervis. The one in the book has an arch over the bird. What is missing on our shard is the word "BROTHERS" after Clementson. 'ROYAL PATENT STONEWARE' in the middle. The word 'HANLEY" is below. There are laurel wreaths to the right and left. And ribbon-type adornments along the base.
***All shards are found in mostly Eastport and other downeast areas of Maine. Mostly shorelines.