Some clouds don't fit easily into any category, and this is one of them. This cumulus humilis cloud appears to have a cap, or pileus, of frozen moist air over the top. Pileus clouds are usually seen over high cumulus congestus clouds. It also resembles a lenticular cloud - there were several small lenticular clouds to the east - but if it is, it must have travelled some distance as they're usually formed over hills, and the only hills around here aren't much more than mounds. Whatever you call it, you can see the layer of ice crystals on top.