I remember now finding a few that looked slightly odd when I was dumping them in the pond. I just figured it was a birth defect or something though. lol
Hmm... Really, I don't know. They look exactly like the darker-shelled l. stagnalis photos I've found, but I don't know what's typically found in the US to compare it to.
Weird better describes the looks you get from family members when you run in the house all excited with a cup 'o snails, rambling almost incoherently about how awesome they are.