Not all fish from the Neolamprologus genus are shell dwellers. There are a few that make their home in shells, though. The ones that I see most commonly in fish stores are meleagris, occelatus, brevis, and multifaciatus. Here is an interesting group discussion on shell dwelling cichlids http://www.petsforum.com/cichlidroom/talks/c002.html
The N. tretocephalus is a rock dweller as is the N. brichardi/pulcher (these are, by the way a very pretty fish, the brichardi, I mean).
I like the A. compressiceps bacause they are a very rewarding fish to keep. They are very slow growers and can take up to three years to reach full maturity. Because of this they are expensive. A mature adult can cost up to fifty bucks. A baby compressiceps of about an inch long sells for around $10. They are unique in size, shape, behavior and attitude. The males get to about four inches and the females a little smaller, but when they turn sideways, they are maybe a quarter of an inch wide, hence the name compressiceps. I could go on and on but I won't bore ya.
Another fish that is a close relationship is the A. calvus. My appreciation extends to this species also. They are almost the same as the compressiceps only not quite as tall.
Well, that's enough.........