sally lightfoots mating or not

[atoz]

I have a 55 gal tank with 4 fish and 4 sally lightfoot crabs. Yesterday It looked like 2 of them were mating but I don't know for sure since I don't know how they mate. This is what I saw

[hr]
1 crab was laying on it's back and another one was laying on it. Body to body. Their was no fighting or anything wierd. They stayed like that for 10 min then the one on the bottom scooted out and went back to eating algae and the one on top went back eating algae. Today all is normal. Does anyone know if they were mating or doing something normal I haven't seen before. If they were mating do they lay eggs and how long to expect?

 

[jtirone]

My sallys do that all the time. But mine appear to be attacking each other. One now only has 2 legs on its right side.
yesterday one was laying on the other. It looked like it was trying to pull the others eyes off.

 

[mr . salty]

I'm thinking some show of aggression, or domminance. The looser is the one on the bottom. STEVE