I think you had poor quality bulbs. I have had clusiana cynthia in my garden for a number of years. I do replant / replenish them because I also grow caladiums there in the summer. I have the species tulips on the outside edge of a circle bed. But still, I dig around and plant other things there and grow lush caladiums in deep shade all summer long.

Still, mine return and are lovely. The bulbs are much larger than pea sized. I'm mooting around for something common as a shape. Everything I can think of (acron in it's pod from a live oak, wooden bead etc is variable.

How about this: Make a circle with your thumb and forefinger. Overlap the thumb so the thumb joint and the top joint of the fore finger are touching. That's the approximate size of the bulbs I planted.

Order from a reputable online vendor. Colorblends gives the bulb size for Lady Jane (about the same size and cynthia) as 6-7cm for Clus. Tubergen's Gem as 5-6cm these are the smallest sizes they sell.

I tried my first species tulips from a big box store in a little plastic bag. They were pea sized and never grew.

Here is a link that might be useful: species tulips

So, about the size of a standard marble? Mine were from Davids & Royston, via a retail nursery, about 15 years ago. I noticed that the nursery carried a different brand of bulbs the following year!
Your climate is still a little chillier than mine, but it's good to hear that they're doing so well for you!
Thanks! : ])

Yes! a plain old marble, only long like a football...sort of.