DaveC wrote:
http://imgur.com/KWFIN1H

Pins 12 and 13 have a little triangle next to the pin; pins 1, 2, 15,
16 have what looks like an "n"; 3 and 14 have an "x".

What's the meaning of these marks?

That's the IEEE standard schematic notation touted by TI in the 80's.
The downward sloping triangle means logical inversion, or active-low. I
don't remember the others.