Astrophytum (Bishop's Hat) is a (mostly) star shaped cactus from north/central Mexico and southern Texas, USA.
Ariocarpus is one of the treasures of the world of Cacti, from Central to Northern Mexico and Southern Texas.
From Mexico and Southern US. Usually having heavy spination and relatively small flowers, the fruits are copiously woolly. Includes the "Golden Barrel Cactus".
Melocactus are recognizable by the large cephalium that develops on mature plants. They are native from Brazil to Southern Mexico, including the Caribbean.
Parodia is a genus of cactus native to the uplands of Argentina, Peru, Bolivia, Brazil, Colombia and Uruguay. There are about 50 species, many of which have been transferred from Eriocactus, Notocactus and Wigginsia.