Early American plays. Part I (Colonial and Revolutionary) : a list / compiled by Ben Russak. (OCLC #22643908)

Anyone know what happened with this call number? I’ve never seen a bare letter after the number like that:

    PS341Z .R87 1936

I’m planning to change it to:

    PS341 .R87 1936

which is American literature, Drama, 17th-18th centuries. Colonial period.