Help!!!

i've tried searching for help with replacing an old door knob online but so far, none address my particular knob. the knobs themselves are out. my problem is with the latch: it just has a flat ring around it and there aren't any screws to remove. at least, none visible to me. here's a picture: [IMG]http://www.tofupicnic.com/latch.jpg[/IMG] not a terribly good picture but i hope clear enough. anyone seen these before? any ideas? thanks!!

I just moved into a house that had the bedroom sliding door replaced, but it was not finished out. The door sits flush to the outside wall so adding out side trim will not be difficult. The problem is the inside. The door sits recessed in to the existing wall and you can see the cut ends of sheet rock and opening. How do I trim it out??? Can some one direct me to the right information or pictures??? I can usually do the work my self if I can see examples. I can not seem to find anything on completing the trim on the inside of the house after a sliding door has been replaced. Thank you for all input.