"striped" Duofold.
Series ran 1940-1948
Your model variably labelled in Parker literature as "sub-deb" and perhaps "lady sacless" models. It is my belief based largely on observation that the great purge of lower price point Parkers in the early 1940's saw this particular model in the Sttriper family vanish around 1943. Still researching that.
Cost $3.95 in its day and was the entry level to the vac-filling Striped Duofolds, noting that button fill pens could be had for $2.95.
Each trim style came in two sizes at same price for each size.
Three (more or less) total sizes of pen can be found as most of the models (being non-blue diamond) were found in what we'll call "Small" and "Medium" with medium thus being the larger of the two sizes for each of these model pairs.
Blue Diamond pens (larger Senior and smaller Ingenue) were found in SMALL and LARGE. Thus the only example of the third and largest size was the larger of the pair of blue diamond pens, both of which ran $8.75 back in the day.
Watch out for stripers. They are addictive.
regards
David