The sides of the pronotum in this one are sort of uniformly rounded, more like Sphaeroderus than the posteriorly-constricted pronotum of Scaphinotus, at least that's what they seem like in these images. The Scaphinotus pronotum reminds me of a king's crown with a top-heavy look.
The lengths listed for the above specimens were, in order: 12, 30, 12, 16, 14 mm
Both genera are in the same tribe (Cychrini) and both eat snails. Is that an egg on the pronotum - maybe from a parasitic fly?

I don't think I've ever seen a Scaphinotus that small, and overall it looks more like Sphaeroderus.

Thanks to everyone for the help. It's tough to see the difference but I do see it. Need lots more experience at it.

I looked at the link to the Canada site. The pronotum is more rounded and a little wider than the Scaphinotus sp. I am stuck between the S. canadensis and the S. stenostomus lecontei and maybe even the S. nitidicollis. Knowing I got that close with it is great. I found it crawling across my kitchen floor at night. I bagged it till morning, chilled, shot, and released. I don't believe the white mark was a parasite as it wasn't 3 dimensional but rather like some pigment mark.

Thanks. The Snail-eating Beetle sure looks the closest to what I can see. We do have a ton of those land snails without the shells. That would work as a food source, right?