I'm certainly not an expert, but based upon what I've read in the past, those are what is commonly referred to as Altolamprologus calvus 'black' or 'black congo'.
A lot of calvus variants can become quite dark at times, so it becomes difficult to really know which variant/collection point we have. That is, unless you purchased wild-caught specimen from the collector.
Again, from what I've read, the one "darker" variant that sets itself apart is what is referred to as the 'ink fin'. This fish's pectoral fins will ALWAYS be dark black and never present a transparent look, like the others will. Based on your second photo, and IMO, you can rule out the 'ink fin' variant.
Just got to let you guys know,there a new calvus on the market called Black Congo White Pearl,similar to ink fins,but you can greatly see the differnce,whith the strain,white dots being more visable,with a bluish ting at the mouth,and body,strain wise could be diffrent as the black,to copper brown bands,but as the white pearly calvus,theres now congo white pearls,collection point?i would never tell lol