When you contact a Locksmith they will ask you what type of lock it is. This can be confusing to some so here is a small list of the basic types. This may help you identify your lock and pass the information to the locksmith.
Yale Nightlatch
Comes in different shapes and sizes but all very similar.
Nightlatch
Comes in different shapes and sizes but all very similar.
Oval Cylinder
Also Avaliable as thumb turn.
Mortice Lock
Standard type lock.