MOSFET Symbol Confusion
Both kinds of symbols are commonly used.

The second set is more detailed, showing the substrate connection explicitly, and the arrowhead indicates the polarity of the channel. Think of it as a diode, where the point of the arrow denotes where the N-type material is. Therefore, the N-channel device has the arrow pointing toward the channel, while the P-channel device has it pointing away.

The first set is a simplified version that does away with the explicit substrate connection. Instead, the arrow shows the direction of conventional current flow, similar to how it is used on BJTs. Therefore, the N-channel device shows current flowing out of the source connection (analogous to the emitter on an NPN) and the P-channel device shows it flowing into the source connection. When you're drawing dozens or hundreds of devices for an IC schematic, this shorthand notation saves time and reduces clutter. You can generally assume that the substrates are connected to the most positive (P-channel) and most negative (N-channel) voltages available on the chip.