Determination of the detailed tree structure showing both recent and historical (from the Bronze Age forwards) connections for those who test positive for SNP R-Z16526 or one of its equivalents. This project was formerly known as the R-P314 Haplogroup Project. P314 (aka P314.2) occurs in a second bottleneck group of 'equivalent' SNPs further down the tree than Z16526 and its own 'equivalents'. Beyond a cluster which is negative for SNP P314 and its equivalents ('Group 1') and where Griffith is the leading name, the tree divides into two; those who have a 12->13 mutation at DYS 617 ('Group 2') and those who don't (Groups 3 and 4'). The latter includes a number of the surnames (and variants thereof) Campbell, Eubank(s), Higgins, Kennedy, Leahy, Martin, McAllister, Porter. Within Group 3, the project embraces all McCarthys and O'Callaghans (and variants) who have test or are predicted positive for SNP L362: the 30% of McCarthys who are assigned to R-L21 Group B in the McCarthy Surname Study and 11% of all O'Callaghans.These share ancestry in Ceallachán of Cashel (died ca. 954 A.D.).