The serial number also appears at three locations on the lids of case & back of the works(on two of the three it appears above the number "36") Other than the script inscription "Pennsylvania" (at 2 o'clock) there are no ther visible markings on the works.

Dial

The style of the movement plates and bridging look like 1875-1885 Longines. The diameter of the case would help some.

David:

Case diameter is 2-3/16 inches.

David, your watch looks to be of swiss origin. It has a Longines look to it but I don' think it is. Looks 1880'ish, are there any other markings on the case?, like a hallmark of some kind.

Some VERY interesting observatins;
A. This is made for the U.S. market as ther Name "Pennsylvania" is strictly American, to identify the forest(land)s of Willimam Penn, hence Pennsylvania.
B. This is NOT a "swiss fake" as some with this name which were direct copies of the Waltham Model 1857!
C. Extra confirmation that this is for the U.S.A. market are the mounted Jewels, considered more popular in the U.S.A. market, otherwise this would have had unmounted "Swiss style" press jewelling.
D. This is NOT a Longines for two reasons,
Longines Serial numbers this low were quite different Key Wind design Movments.
The reinforced covering of the Crown and click wheels was never done on Longines watches.
E. For the time (1880's or earlier) this was quite "High end". If there is no makers type marking on the case, it is deserving (at least) of a look under the dial to check for a makers name and a service as well.

Ray/David: Thanks for your input. I "remeasured" the case--it's more accurately 2-1/4."

Ray: Sorry-forgot to say there are no hallmarks on the case.

That is an interesting watch and appears to be a higher grade. I think it looks like an Agassiz movement but that is strictly a guess.

My first thought might have been Longines as was mentioned earlier. The Longines flying hourglass logo although registered in the late 1880's, was oftentimes used as ealy as the late 1860's on the movements produced in the Longines factory. Although your watch has some quality features, one that is not present, but found on higher grade watches of the time are Wolfs Teeth winding wheels that would have certainly been used by Longines in the times your watch was likely made. Like Dave Abbe added, a look under the dial would be interesting as sometimes the winding/setting mechanisms can tell alot and maybe some markings under there as well.
Also, the lack of case markings is a puzzle as it looks like the case could be original to the watch but i would have expected some hallmarks or initials of some kind if foriegn made and a makers name on it if domestic.
Keep searching dave, it may take a while but somethings bound to turn up. The searching for information is part of what makes this hobby fun.

I went over the watch again with a jeweler's loupe. On the inside of the back cover (to the works), there are three "marks" (spots?) see picture--one in the center, one about 3 o'clock and the other about 10 o'clock. They are certainly not distinct hallmarks and (perhaps it's just the suggestion and it simly doesn't make any sense) but where hallmarks had been removed (worn off)?

I also discovered what looks like some very faint numbers? and letters? that had been scratched, seemingly, free hand on the inner ring of a lid. But they are too faint to be be read. I tried to enhance the legibility of them by rubbing some graphite over them to see if that might help but no luck. Have no way of knowing if it related to (done by?) an owner, someone who might have serviced the watch at some point. LOOKS (and it's a stretch) like "94-05" and then something "else".

The small etched numbers are probably service marks. The other marks could be , or might have been hallmarks. They are in the right places anyway. It's too bad someone felt the need to remove them.

Dave, can you post a picture of the movement looking straight into it like your dial photo. And maybe a close up of the balance/escapement area if possible?

Ray: I'll work on the picture. I've found natural light to work best and it's raining/cloudy here today...

Ray:

A couple shots to view

And another close-up