In view of the birth of abnormal Texel lambs sired by a single ram, experimental matings were carried out to determine the extent to which the malformations shown by the lambs were clear-cut inherited defects and, if so, which was the mode of hereditary transmission. From investigations on six abnormal lambs and a study of the literature it was concluded that these were inherited defects not previously described and marked by cheilognathoschis which was almost invariably associated with an unduly light birth weight, brachycephaly and cardiac septal defects. The placenta of one of the abnormal lambs, which was studied, showed marked changes. The proportional numbers showed that, when the more complicated inheritance patterns are not taken into account, the defect is transmitted by a recessive autosomal gene.