Notwithstanding their simplicity, these forms are practically confined to North America. Their strong individuality proves that their present distribution must be due to mutual influence among various North American cultures. We cannot determine where the pattern originated but it is quite certain that its present distribution is due to cultural contact; its occurrence is probably related to the use of stiff rawhide for receptacles, to the method of painting used by the Indians, and to the old method of decorating with porcupine quill weaving and embroidery. I have called attention to the difference in arrangement of these patterns among a number of tribes and A. L. Kroeber, R. H. Lowie, and Leslie Spier[97] have discussed these questions in greater detail (fig. 151). The parallel stripe arrangement is characteristic of the Arapaho; a central field surrounded by a square, of the northern Shoshone. Owing to the close contact in which these two tribes live at the present time, which favors intertribal trade, the distribution is not quite so clear as it has probably been in earlier times. [97] Leslie Spier, An Analysis of Plains Indian Parfleche Decoration, University of Washington Publications in Anthropology, Vol. I, pp. 89 et seq. where the earlier literature has been quoted. [Illustration: Fig. 151 _b_, _c_. Types of parfleche and pouch painting, Shoshone.] [Illustration: Fig. 152. Arapaho designs.] [Illustration: Fig. 153. Sioux designs.] Certain differences may also be observed in the arrangement of bead embroidery the forms of which are very uniform over an extended area of the western prairies. A characteristic form of this design consists of a central diamond or rectangle, from the corners of which emanate lines that terminate in triangles facing the central field either with the apex or with the base; sometimes a crossbar with prongs is found at the end of these lines. Among the Arapaho (fig. 152) these patterns appear singly on a plain background; among the Sioux (fig. 153) the central square is seldom used. While among the Arapaho the lines are usually attached to only two opposite ends, the Sioux almost always attach them to the four corners of the central diamond. Furthermore, the Sioux like to vary the background by inserting stars or crosses and the design seems to occur more frequently symmetrically doubled than among the Arapaho. Another good example of differentiation in arrangement and identity of pattern elements is presented by the basketry of the Indians of British Columbia. Among the Thompson Indians the design elements are distributed evenly over the whole side of the basket; among the Lillooet they are confined to the upper part of the side while the lower part remains undecorated; among the Chicotin there are three bands of decoration along the upper part of the basket (see p. 297).