The porcelain plates seen below were made in Europe in the 1890s.  They were used for clams and other seafood. 
These are larger in diameter than the smaller plates that match them that went at every place setting.  They were used just for clams or any other things that would nest in the wells made just for this purpose.
Similar to oyster plates made just for oysters, these differ in that the well made for the oyster is more oval in shape while these being made for clams are round.
They are highlighted with gold which was the telltale sign of them being special, at least at the turn of the century in America. Gold remains a symbol of wealth, luxury and importance.
These plates were made by well know porcelain manufacturers in Europe and in America. The service of seafood was popular and made for an entire genre of things made just for their service – so much so that oyster plates, clam plates and lobster dishes are even more collectible today. 
I know of many, many collectors across America and in other countries who have a collection of oyster plates and other such plates hanging as decorations in their dining rooms and kitchens.  Many were decorated by talented porcelain painters who represented some of the finest paintings ever done without the use of traditional canvas or board. Sea food plates were a big deal, highly prized and remain so today.
An easy and elegant meal would be to steam or bake some clams, remove them from the oven ware you cooked them in and place them in these plates. 
The effect is beautiful and the ease of use these plates provide due to the well is appreciated by your guests. 
I often use the ones I have for garden tomatoes as the variety I prefer are smaller than the large heirloom varieties. 
Tomato slices from my home garden fit perfectly on these plates. 
I make a salad every summer that my family in Charleston always made. It never occurred to me as a child that it was anything special. Now that I am older, just the scent of it takes me back to childhood.
I have published this recipe in several books on entertaining and I hold close to my heart as it reminds me of home.
Charleston Tomato Tower
2 yellow tomatoes
2 red tomatoes                  
Use ones similar in size for best results
Skin and slice about 1/3 inch thick
Salt and pepper
Beginning with the largest slices, place one down on the dish you will serve it on.Use a dinner-size plate as there are a lot of garnishes later. Add 1/4-inch thick slice of fresh mozzarella (in plastic tubs in liquid).
Alternating colors of tomatoes and slices of mozzarella, end up with a “tower” of about 4 slices of each.
Insert a wooden skewer or rosemary branch into the center, passing through all the layers to hold your tower together.
Whisk together your favorite olive oil and vinegar (enough to put 2 or 3 tsp over each tower), add salt and pepper.
Garnish each tower with chopped red onion, chiffonade of basil, goat cheese crumbles and crumbled cooked bacon. 
Pour the oil and vinegar over them.  
I always have small yellow, pear tomatoes in my garden so I also halve them and stand them around the tower. It is beautiful and so good – a true taste of summer. 
Using small garden tomatoes allows me to serve these towers on clam plates. They are truly beautiful and aromatic on a buffet. 
Simple things are often the best.