Neoporteria. I bought this cactus several years ago because I liked the white spines, but was very pleasantly surprised and pleased when it bloomed-and bloomed and bloomed! The flowers last four or five days, and it will bloom off and on all year. So I highly recommend this one for your collection. In the past it has displayed up to seven flowers at one time.
Bright Lights of Muleshoe
Cactus Are Cool