One of my best friends from grade school moved to Argentina back in the Peron days. With her wealthy father, who was probably "connected", if you know what I mean, she settled down into a house with glass floors. She brought photos of the place by, and you could see all the way down to the first floor from the third. Weird...
What you've got there is the "full Boehm" version of an early Selmer instrument. This is one of the ultimate developments of the so-called Boehm system of the instrument, and it has all of the optional key work found on normal clarinets. They were common as recently as forty years ago, with both Selmer and Leblanc selling them, but of late can only be purchased from one or two manufacturers, and none of the "principal" ones.
The reason for the lowest key touchpiece on the horn is the rational behind the "full Boehm" instrument in the first place. With this horn, you can play both Bb parts and A clarinet parts, all on the same instrument. Without it (or an A clarinet of your own), good luck playing Peter And The Wolf in the original key, and several principal clarinet players of my acquaintance have found in the past. (It then fell to me, the lowly third/auxiliary/bass clarinet player to step up and take all of those prime solos.)
By the way, we bass clarinet players play a double sized version of this instrument. On the up end horns, the additional key work (the Ab/Eb lever, the articulated G# key, and the low Eb key (discussed above) are all routinely provided on the professional level instruments. And, that is because when we run across an A bass clarinet part, we have to be able to transpose it, as only .0001% of us own an A bass clarinet. (A pair of orchestral clarinets (A and Bb) weighs in at about to ten pounds - a pair of similarly keyed bass clarinets would weigh about as much as a medium machine gun plus ammunition.)
From the inscription that you give, it is obviously an instrument from before the Selmer firm really got started with full blast marketing of their own horns here in the US of A. Figure 1920s or so. The old style, assembled case also points in that direction. Buy a new case and keep it disassembled, this to prevent damage to the center tenon. (Also, the center tenon, with its hole through the sealing cork, is a source of leaks on these horns, Make sure that the cork is intact and reasonably plump to prevent this from happening.
I'd be willing to bet that, despite the apparent age of the instrument, it is a low pitched one. Other than a "L" or "LP" or some other inscription, the best way to tell is to play it against a tuner and see what the true pitch is when you play the long B (thumb on the ring and the register key|six fingers down on the rings| plus the bottommost upper key for the little finger on the right, and the one farthest to the center of the horn for the little finger on the left. If the tuner shows something pretty close to a concert A natural, then you've got a low pitch horn.
Over the past sixty years, clarinet teachers have discouraged use of this extra key work, although over the last fifteen years or so they have recognized the utility of the alternate Eb/Ab key for the left hand little finger (and, as a result, it can normally be obtained as a special order item on regular professional instruments). I have played a pair of these for over fifty years, and have noticed no diminishment of the tonality or facility of the horn, but that's just me. (I also don't like the bog standard R-13 from Buffet, so go figure.)
From the looks of the mouthpiece cap and the ligature, it appears that the horn is silver plated, another plus in the overall scheme of things.
From the brown "rust" on some of the joints, it looks a lot like a clarinet with an ebonite body (hard rubber, containing (among other things) a smidgen of lead), but from the end of the joint shown, I'm sure that it's just a poorly maintained wooden one. If wood, it badly needs to be oiled.
Cracks? Condition of the pads? Both of these are critical to the sale value. The appearance of the horn is critical to the curb appeal.
If crack free and in otherwise good condition, I'd buy it in a heartbeat ...if I didn't already have a lifetime supply of backup instruments. Similar instruments on eBay go for upwards of $700.00, although I've not seen one of this vintage for some time.
EDIT: Ooops - I just took another look and noticed the one-piece body of the instrument. Those are very rare in wood (because of the difficulty of getting a solid joint of the grenadilla used to create the body). So, it may well be (due to the one-piece body and the brown smut on the surface) that you do have an ebonite horn. It would not have as much value as a wooden one.
