Upon retirement of a member for nonservice connected disability, he shall receive an annual pension, payable in monthly installments, dependent upon the aggregate length of his service, as follows:

After 10 years but less than 12 years of service, seventy-five dollars ($75) a month.

After 12 years but less than 14 years of service, eighty dollars ($80) a month.

After 14 years but less than 16 years of service, eighty-five dollars ($85) a month.

After 16 years but less than 18 years of service, ninety

dollars ($90) a month.

After 18 years but less than 20 years of service, ninety-five dollars ($95) a month.

After 20 years of service, one hundred dollars ($100) a month.

A pension for nonservice connected disability shall not exceed one-half of the terminal salary of the member.