Yes, Simon, it is M. prolifera, but I don't think that it can definitely be named as ssp. texana. According to Pilbeam, there are two variants of texana, one with brown tipped spines and the other with yellow spines. However, ssp. prolifera itself also has pale yellow spines.
Which is yours? to be honest I can't really tell the difference, so I can't say. Maybe others can help resolve this.