Considered a cultivar of Rebutia marsoneri, this fine white spined beauty offsets prolifically and gets to about 4 inches tall and 3 inches across. The flowers are usually red, or reddish orange, but rare yellow flowered cultivars exist. I have a yellow one and then later got some red ones.
      I got this one this spring and planted it in the garden. It flowered several times for me and formed some little offsets by late summer. Click below for more pictures

Flowering in spring

Another view

Flowering in the garden

One of the red ones