Cat-Faced Spider - Araneus gemmoides
Also called cat spider or jewel spider (Canada) or barn spider. Araneae (Spiders) » Araneidae (Orb Weavers) » Araneus
This beautiful orb weaver was photographed at Sanders County, Montana.

The markings on this spider's back are thought to resemble a cat's face, complete with bumps that look like ears. I'm not sure if you see the cat by looking from the front of the spider or the back; see what you think. This is a fairly large spider, about 20mm, or almost the size of a quarter dollar. Its habit of building its large orb webs inside barns and outbuildings, and near light sources causes an inordinate number of human encounters. It is completely harmless.