Before Harry Bettoney arrived in Boston, Theodore Berteling had been making woodwinds in Boston for a few decades. From what I could find, he was more known for his flutes than clarinets. There is only one post about one of these models (close serial, too) on the BB. That report indicates use in a high school all state band conducted by J.P. Sousa. Apparently it was at least a decent student instrument in that time. If the serial number is indicative of production numbers, there are not very many Berteling clarinets. This one is late production and only number 4574.
T. Berteling & Co. moved from Boston to New York and continued to make instruments after Theodore died ceasing production in the mid 1920s. This clarinet is an Excelsior model most plausibly from around 1920. It is low pitch but has no designation of that anywhere. Like the H. Bettoney models of the same era, I found strong French influence. The keys are still very tight, mostly it needs pads and corks to play. The more I look at the keys, I don't think I will polish them. The patina is different from most tarnish and sparkles in the sunlight. I think these are nickel silver.
There are a few details to note that place it historically. It has the flat spring under the RH5 F# key, a shared lever post for the LH5 F# & E. The C# tone hole on the upper joint is flush to the exterior of the joint, not cut in. And of course the elegant spiral register key. The key work style and quality could pass as French.
Note that the spiral register doesn't have the little pointed corner at the first bend that is more common on French spiral register keys. The wood has the look of oil dry grenadilla right now. Cleaning, oil, pads and corks to get this one playing. There were two minor barrel cracks that I have already glued as of these photos, nothing too serious wrong here.
See the T. Berteling ad in the same column with Moennig, Meinell, F. Lauter, and Konig & Simon.
I found a catalog page with Bertelings. This one is the #7 and sold for $60 whenever this catalog was distributed. It is probably about the same given that the illustrations show the spiral register key and the marks on the clarinet show Carl Fischer as the distributor. The comparable Carl Fischer house brand was $47 at the time.