The category of ‘selection patents’ pertains to specific inventions that are individually novel but selected from a group of a previously known class, and shows some surprising or unexpected benefits. Although selection patents are mostly seen for chemical species/compound, selection may also be made from a numerical range such as temperature/pressure conditions in production methods.
Selection Patents: to patent the non-enabled advantageous selection? By Preeti Sharma
http://www.ippromagazine.com/ippromagazine/IPPro_issue_020.pdf