Atrium Door Hardware, Lever Style Brass Mortise Lock.
The Atrium lock hardware -set includes everything necessary for replacement, including screws and strike plate.

Levers: 4 -1/2 Inch Solid Brass Mortise Lock
Backset: 1-3/4 inch (45mm) narrow stile
Door thickness: 1-3/4 inch
Lock faceplate measures: 15/16 by 9-5/8 inches.
Handle Escutcheon Plate: 1-3/16 x 8-1/4 Flat, 3 screw holes, solid brass
Cylinder Type: Single cylinder lock, Crescent thumb turn inside.
Atrium Keyed Cylinder: rekeyable Schlage SC-1 keyway with 2 keys
Spindle for handle: 5/16 (8mm) x 3-1/4 inch (83mm) on the Square.
Distance from the center of handles to center of Cylinder 3-5/8 inches (92mm)
Handing: This handle set can be used in Left and Right hand applications.

Color Options:
Polished Brass
Polished Chrome
Satin Nickel

For help with installation of Atrium locks, please read The Atrium Lock Installation Instructions. 

Priced and sold each.

Resources:
General Information on Atrium Doors: Guide to Atrium Doors
Guide to Installing Atrium Locks: How to Install an Atrium Lock