It may indeed be a Tessar, it is a classic type, but there are other 4 element types, and also diameters in relation to aperture stop, and the position of the diaphragm. Elmar are similar, as are Industar etc.
Just because it has four elements does not always mean a Tessar type. The Elmar was originally a five element lens, but the rear three were combined to two as glass improved, ending up very close to the Tessar.
The XA-1 was a modest aperture which made the coverage of 24x36 easier, and indicates it is a Tessar, although Minox got F2.8 on their Tessar in the Minox 35mm, by using special glass. Usually you cannot get more than F2.8 on any Tessar. Stephen.