Size: Marked as Ladies 40 - but I really don't know what the sizing scale is.
I assume this is the maximum seat/hip size: 40 inch hips?
The actual garment measurements (unstretched) are as follows:
Bust.............26 inches (unstretched)
Waist...........24 inches (unstretched)
Hips.............30 inches (unstretched)
Woollen bathing costumes were notoriously stretchy, and had a tendency to sag when wet, as they retained water.
That is probably the reason why these were designed with a little modesty skirt round the hips.
(Both men's and ladies' costumes had this feature).
The famous Jantzen "Diving Girl", in her 1930s incarnation, appears on the skirt, and also on the label of this garment.