Instructions from 1950’s Semco Crochet booklet
Note: these instructions use UK/Australian crochet terms.
SHELL (sh): May be worked with tr, d tr, or longer, stitches. They are made up of a given number of stitches on each half, separated by a given number of chain stitches.
When worked on a foundation chain, a given number of stitches are skipped. When worked over another row of shells, each one is placed in the chain between the halves of the previous shell, or between two shells.
In the illustration, the directions would be as follows: Having a chain, allow 3 for the first tr, two tr in 4th chain from needle, ch 2, 3 tr in same chain as last tr, * skip 5 ch, in 6th ch work, 8 tr, 2 ch, and 3 tr. Repeat from * across row. Ch 3 and turn at end of row. Second and all other rows, shell in shell.