sex of black mollies

Question
i bought 2 black Mollies yesterday. i asked the pet store lady what gender they were and she said "only another fish would know" which was less then helpful. i looked on the Internet and found that u can tell them apart by the males anal fin. and despite a rather unhelpful photo which seemed to point this out which i compared to a female one and again found no difference im not sure what this is. both my fish appeared to look exactly the same however when i looked through the top of the tank one appears to have alike a thin line of fin looking thing between its big back fins, now whether this has just broken away or whether it is the anal fin i don't know. they both have these two like mini fins by what I'd call their anus underneath their 2 big tail fins but i think what i should be looking for is just one fin and a detailed explanation or picture would be greatly appreciated.

Answer
hello Hannah,

I understand your frustration. So pretty much here is how it goes. If the Black molly has three fins on the bottom of it this is a female (two in the front and one in the back) and fish with only two fins in the front are male fish. Did this help at all?

Thanks alot,
Michael M