Much of Manhattan is a numbered street grid, with the exception of lower Manhattan below Houston Street, Greenwich Village, and many streets far uptown in Inwood and the Dyckman Street area. However, while most of Manhattan’s cross streets are numbered, you’ll occasionally find one-block stretches that used to have a name: for example, Charles Street between Bleecker and West 4th Streets was named Van Nest Place, and West 29th Street between 8th and 9th avenue has been called Lamartine Place in the past. (A comprehensive list of former Manhattan street names can be found at Gil Tauber’s Oldstreets.com, and of course there’s the old standby, FNY’s Street Necrology pages for selected areas around town.) A surviving example is St. Luke’s Place, which is a portion of Leroy Street between 7th Avenue South and Hudson Street in the Village.
One such “subname” is Dunscomb Place, which appears on this Manhattan map from 1908 as East 50th between 1st Avenue and Beekman Place. I’ve seen it on maps as late as the 1960s, but the name was probably dropped at least by the mid-20th Century. It was always a “subname” and never replaced the actual East 50th Street official name.
It’s likely the buildings that line East 50th are the originals from the late 1800s. “Dunscomb” is a British place name derived from Welsh and Old English words for “fort” and “valley.” The Mitchell Place shown on the map is “alive and well” and ascends a hill between 1st and Beekman.