The significance of the looped figure which forms so prominent a feature in the designs in question has not been determined. I would offer the suggestion, however, that, from the manner of its occurrence, it may represent an inclosure, a limit, or boundary. It may be well to point out the fact that a similar looped rectangle occurs several times in the ancient Mexican manuscripts. One example, from the Vienna Codex,[142] is presented in Fig. 5, Plate LIX. It is not a little remarkable that a cross occupies the inclosed area in all these examples. [Illustration: PL. LIX--THE BIRD. 1. Shell gorget from stone grave, Tenn. 2. Shell gorget from stone grave, Tenn. 3. Shell gorget from stone grave, Tenn. 4. Bone implement, N. J. 5. Design from Aztec painting.] I shall close this very hasty review of the bird in the art of the Mound Builders by presenting the remarkable example of shell carving shown in Fig. 1, Plate LX. Like so many of the National Museum specimens, it is practically without a record--a stray. It is labeled "B. Pybas, Tuscumbia, Ala." It is old and fragmentary, the shell substance being, however, quite well preserved. It is the right-hand half of a gorget which represents an eagle's head in profile. The skill of the ancient artist is shown to great advantage; nothing can be found, even in the most elaborately carved pipes, equal to the treatment of this remarkable head. To overcome the difficulty of cutting the flinty and massive shell was no small triumph for a people still in the stone age. To conceive and execute such a graphic work is a still more marvelous achievement.[143] The lines of the mandibles and protruding tongue are strongly and correctly drawn. The eye and the markings of the head are executed in smooth, deeply incised lines, and are conventionalized in a manner peculiar to the American aborigines. [Illustration: PL. LX--THE BIRD. 1. Fragment of shell gorget, Alabama. (1/1) 2. Gold ornament, Florida. (1/2) 3. Head of ivory-billed-woodpecker.] THE SPIDER.