Arachnology geeking

I was taking a nap in the afternoon, and looking up at the ceiling, I saw a nasty looking black and red spider crawling right overhead. I felt a little uncomfortable as it crept down the wall towards the edge of the bed, so I got up and caught it in a jar. It was rather aggressive, attacking the prongs with which I had attempted to grab it at first. Once caught, I could inspect the spider species...