Absence of the d triradius.

Ten cases of absence of the d triradius are reported from a heterogeneous collection of dermatoglyphs from 3610 subjects. There was one case in 1000 normal' controls. There were three cases in a group of 800 subjects with congenital heart disease. There were two cases with the 49, XXXXY constitution, a previously noted association. A pair of probably monozygous twins were discordant for absence of the d triradius. The condition was left-sided in six cases, right-sided in one case, and affected both sides in three cases.