There are two series of cases which strongly corroborate the theory of the effect of the exogamous organization on the kinship nomenclature. They constitute a distinct variant of the Dakota principle, the deviation being in the designation of cross-cousins. While these are still differentiated from parallel cousins, they are not placed together in a single category but are classed, one group of cousins with the first ascending and the complementary group with the first descending generation. In short, the generation factor which is fundamental in the Hawaiian scheme and only modified by dichotomy in the usual type of bifurcate merging schemes is here overridden by some other factor. Now what is the nature of this new determinant? Let us look at the facts. The Hidatsa class the father’s sister’s son with the father and the father’s sister’s daughter and all her female descendants through females to infinity with the father’s sister; correlatively, the mother’s brother’s son, in the absence of special words for nephew or niece, is classed with the son, even by women. That the Crow scheme is almost identical, is readily intelligible from the historical relations of the two tribes, who speak very similar languages of the Siouan stock. But the essentials of the classification reappear among the geographically, linguistically, and culturally remote Hopi, with suggestions of similar features among the Tlingit and even in Melanesia. We are again confronted with a puzzling problem of distribution. An analysis of the Hidatsa data clarifies the situation. According to the statements of the natives themselves, the term ‘father’ is applied to any father’s clansman irrespective of age and would accordingly include the father’s sister’s son. This suggests that the clue to the entire situation may lie in the clan feature. As a matter of fact, we find the daughter of the father’s sister’s _son_ is not classed with the daughter of the father’s sister’s _daughter_. The only difference that can be connected with this distinction is that in clan membership: the former relative, owing to the exogamous clan system, can never, and the latter relative always must, belong to the father’s sister’s clan. Hence the former, being a father’s sister’s son’s, _i.e._, a ‘father’s’, daughter, becomes in Hidatsa speech a sister, while the latter is designated by a word translated paternal aunt’ but really embracing likewise all the lower generations of females in the paternal clan. That we are dealing with the clan factor, is corroborated by the fact that in Hidatsa terminology the mother’s brother, instead of being designated by a specific word, is classed with the elder brother, a term also applied to the mother’s mother’s brother. The last-mentioned kinsman may be similarly addressed in Hopi.