A bit of history...
Snowflake was introduced in 1956 along with Pink Daisy. While Pyrex had been producing solid color opalware for several years, Pink Daisy and Snowflake were the first patterned dishes to be released using the new screen-printing process. They were introduced as “NEW Pyrex Decorator Casseroles” and quickly gained a market with consumers.
One of the selling points of this new casserole dish was its clear cover, meant to be used not only as a cover but as a trivet to protect table surfaces. It could even be used as an extra serving dish.
Snowflake was released in three versions. The longest running color combination was a white pattern on a turquoise background. However Snowflake also came in a turquoise pattern on a white background, and a white pattern on a charcoal background. While the white on turquoise version ran until 1967, the turquoise on white was produced until 1963 and the charcoal version was produced until 1960.

it measures 6.5" by 11.5" and it is in good condition with minimal wear and tear from over the years