There are several white glass-ceramic dishes in the Merry Mushrooms line and, while they all have the same decal pattern on the side, have white bases, and clear glass lids, not all are technically the same type of dish or Corning Ware brand.
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First is an oval covered Casserole, the first one of its kind sold. The brand isn't mentioned in the catalog. It might be Anchor Hocking Fire King brand cookware.

Second is the Casserole Ovenware Set, offered in mid-1970s catalogs. The lids of the round dishes and the oval dish appear to be clear and not dimpled like the other dishes below. Exisiting dishes are also found with undimpled lids which may not be replacements afterall. They might be Anchor Hocking Fire King brand cookware since the mixing bowls offered in the same catalog have been identified as such.

Third are the Covered Corning Ware Saucepans, first appearing in the sae catalog as the ones above. These pans look just like the casserole dishes but have dimpled clear PYREX glass covers, are identified as Corning Ware, and make use of the Corning Ware black plastic transferable handle. It's this handle which makes these saucepans and not casseroles.

Lastly are the Covered Corning Ware Skillets, also for sale in the mid-1970s. Like the Saucepans, these skillets resemble casserole dishes but for the transferable handle that was sold with them. Again, the skillets have the dimpled clear PYREX covers. But, since they are described as skillets, the sizes are given in diameter and not quarts like saucepans or casseroles.