Here are the stages that lead from tummy time to crawling:
1) tummy time
2) table pose (up on all fours)
3) table rocking (rocking back and forth)
4) downward facing dog
5) pushing backward, away from what they want to go toward
6) belly crawling
I found this list in a book today and was pleased to see all three babies are progressing nicely through the steps toward crawling. Elliott and Mazie are belly crawling. Lucia is one step earlier than army crawling; she is moving backwards.
While Mazie and Elliott did some moving backward, Lucia has stayed in this stage for quite a while. It must be rather frustrating to be moving away from what you want to go toward. Here are some pictures of Lucia in various predicaments she has found herself in.