Answer: Fasciola hepatica
Congratulations to everyone who wrote in on this case! You all recognized that this egg falls into the category of thin-walled oval operculated eggs, which includes (in increasing size) Clonorchis sinensis, Diphyllobothrium latum, Paragonimus westermani, and Fasciola hepatica/Fasciolopsis buski. I put the last 2 eggs together since they are morphologically indistinguishable - although they are from 2 distinct flukes that inhabit different regions of the body.
There are subtle differences between these 5 eggs, but they can be easily confused for one another. That is why it is essential to MEASURE your eggs using an ocular micrometer so that an accurate identification can be made. Of interest, these 5 eggs are from 4 flukes and 1 cestode. This just shows that there is morphologic overlap between very different phyla of parasitic worms.