has been a long time since I tried(couple years now) But it is in the way thier shell comes together on thier back if I recall. Did A bunch of research on it when Mine started breeding and Identified my male as Alleni. My female seemed iffy but they could breed so meh. If you search around on line theres lots of info on it. I beleive if the two semi circles from the sides meet they are alleni and if they do not and have a gap they are clarki but dont quote me on it.
In all fairness I would not have been as successful with mine as I was if not for Neale Monks Tripped over him on a different forum when I started out he walked me thru a lot of careing for my crays and pointed me in the right direction. Would probly still be breeding them If my male had not gone crazy and killed everything else in the tank after 3.5-4 years of haveing them.
