Work in public domain; copyright expired in 1991 without renewal. From U.S. Copyright Office Information Circular 15a, Duration of Copyright:

Under the law in effect before 1978, copyright was secured either on the date a work was published or on the date of registration if the work was registered in unpublished form.

From U.S. Copyright Office Information Circular 15t, Extension of Copyright Terms:

Copyrights whose first 28-year term of copyright was secured between January 1, 1950, and December 31, 1963, including works protected in their first term under the Universal Copyright Convention, still had to be renewed within strict time limits in order to receive the maximum statutory duration. U.S. adherence to the Berne Convention did not alter this requirement. Renewal registration had to be made within a year period beginning on December 31 of the 27th year of the copyright and running through December 31 of the following year.

If a valid renewal registration was made at the proper time, the second term lasts for 67 years. This is 39 years longer than the 28-year renewal term provided under the 1909 law and makes the two terms of protection for the renewed copyright last for a total of 95 years. However, if renewal registration was not made within the statutory time limits, these copyrights expired at the end of their first terms and protection was lost permanently.