This is an old-style Pella single-point mortise lock with an 85mm PZ DISCONTINUED
This is no longer manufactured by Pella.

Pella Euro Cylinder with key on outside and square thumb turn hole on inside (thumbturn is part of handleset)
Faceplate width: 15/16 inch
PZ (Handle-to-Cylinder Spacing): 3-5/16 inches (85mm)

We have a kit to replace this lock: part #40177 (lock by itself: part #40176)
Note: Some modifications are required; replacement is not a direct match

See article: Replacing Pella Old-Style Single-Point Mortise Lock
See: Comparison pictures
See video: How to Rehand Pella Replacement Lock