Having been pointed in the right direction, I now see that the
De Kleist & McCormick patent sits in class 226, subclass 138 (and
with secondary assignments as shown in the list).

  226/138; 226/141; 226/157; 226/173; 451/184

Class 226 is not primarily a perforator class: its class definition is
"Advancing material of indeterminate length".  This patent is for the
edge grippers that pull the paper through the perforator, so the
classification makes sense.

The US Patent & Trademark Office web site offers a useful means of
listing all the patents in a particular subclass. The primary link
to this is

  http://www.uspto.gov/go/classification/

You can then choose either a "Class Schedule" that simply lists the
available subclasses, or "Class Definition".  That is the same list
but with a much fuller description of each subclass.  In both of these,
a little red box containing the letter "P" will list all the patents
in the subclass.  Given that there are many millions of patents, the
detail of the categorisation is such that there are often only 20 or
30 patents in a particular subclass in the sort of areas covered by
mechanical music.

The class of major interest for mechanical music is 83 (music), which
should contain all the instrument patents as well as things such as
recording devices including perforators for that purpose.  Perforators
that are purely for perforating and do not mention any other activities
come into class 234.  By following the subclasses from one perforator
patent to another you can build up an idea of what they are about.
Simply browsing all the other patents in a subclass can throw up
fascinating devices.  It would be a good way to waste a few weeks!

The great shame about these old patents is the lack of reference to
earlier patents -- modern-day patents seem to carry many more
references so you can follow the ideas back.

Julian Dyer