These beautiful carabiners were produced in the 1950s through to the late1960s. They were strong and well made with several design features ahead of their time. The graceful arched spine set them apart from other carabiners and the wide flared baskets gave them a triangular cross section which increased their strength. Later carabiner designs would refine the triangle, ovoid, or I-beam cross section concept to greater effect with improved technology. (MSR I-beam carabiner, Petzl carabiners, DMM carabiners)
Sebastian Mariner (1909-1989) designed these carabiners along with several other climbing tools and rescue techniques. He had a keen eye for innovation and the ability to take a climbers needs and turn that into functional equipment. More information on his life can be found here.
The design evolved slightly from the initial models to the final production version:
The stock used to construct the gate grew thicker.
A thicker gate increased closed gate strength and durability. The dovetail gate nose could be thickened and improved allowing the gate side of the carabiner to handle any load transmitted to it without deformation or outright failure.
The sharp angles on the spine were modified into a smoother S-curve.
Either it was recognized that sharp angles were a liability and a potential weak area or changing construction methods precipitated the change.
The wide flare on the baskets decreased slightly.
Climbing equipment was changing. Better ropes and protection were available and a smaller radius could be used on the basket of the carabiner without damaging the equipment. This, in turn, allowed the carabiners to fit through, and hang straight in, smaller eyes then becoming common on pitons. (Period soft iron hand forged pitons usually had rings or large diameter eyes.
See: Sporthause Schuster, Fritsch & co, and others
Also see: Mountain Project