Circular Pocket Cornet by Metzler & Co.
By the late 19th century in England, circular cornets were often called "busker's bugles" but that was likely a slang term attached to them when they were out of fashion and not wanted by any but the peripatetic street musician. During the 1850s and 1860s circular cornets enjoyed a certain popularity when the later form was not so ubiquitous. This example has the added novelty of being very compactly wound and with an oval bell rim making it possible to transport it in a coat pocket or small satchel. Judging by the somewhat rough and worn condition, it may very well have been the property of a street musician at one time.
Metzler was a music merchant in London from the early 1830s and likely didn't manufacture brass instruments there. Other known instruments marked by Metzler include two other cornets like this one, a cornopean and keyed bugle but mostly flutes and clarinets. This cornet was most likely imported from France in the 1860s. It is 6 3/4" long with the shank removed, the bell rim measures 3 1/8" X 4 1/8" and the bore .449". This cornet did not originally have a waterkey and the buttons, mouthpipe shank and mouthpiece are also replacements.