There were 6 accepted species found [distribution filter:
3 Echinocactus parryi Engelm. distributionfilter: global
heterotypic synonyms:
Emorycactus parryi (Engelm.) Doweld;
links:    
IPNI (International Plant Names Index)   
WFO (World Flora Online)   
Google   
Flickr
5 Echinocactus polycephalus Engelm. & J.M.Bigelow distributionfilter: global
homotypic synonyms:
Emorycactus polycephalus (Engelm. & J.M.Bigelow) Doweld;
links:    
IPNI (International Plant Names Index)   
WFO (World Flora Online)   
Google   
Flickr
6 Echinocactus texensis Hopffer distributionfilter: global
homotypic synonyms:
Homalocephala texensis (Hopffer) Britton & Rose;
heterotypic synonyms:
Echinocactus courantianus Lemaire ex Labour.;
Echinocactus lindheimeri Engelm. & A. Gray;
Echinocactus platycephalus Muehlenpf.;
links:    
IPNI (International Plant Names Index)   
WFO (World Flora Online)   
Google   
Flickr