2 is normal as far as can be seen, except that the apices are turned through a small vertical angle. The anterior portion of the pedicle valve is crushed in. No. 12 is normal throughout. It is unfortunate that none of the specimens show the crural attachment of the spiralia. Such structures must certainly vary in order to support the spires in their various positions. The above facts would seem to indicate the following conclusions: First, in those spire-bearing brachiopods in which the form of the shell does not govern the position of the spires, the Athyridæ in particular, the spires may be subject to a considerable variation in both position and form. Second, that the crural supports are probably so modified as to accommodate the spires in their various positions. In the light of the foregoing, it will be seen that in the future it will be necessary to study the structure of several specimens before using small variations of internal structure in these shells as bases for group divisions. One might expect greater individual variation among the Flint Hills specimens, owing to the physical changes that were taking place during the close of the Carboniferous and the early Permian; changes which soon caused this species, together with many others, to become extinct. However, this cannot be said of the most striking case (No. 11) from the Topeka limestone. It would seem that such variations as are found in Nos. 3 and 11 would be decidedly detrimental to the well-being of the animal, though the latter of the two seems to have been a vigorous individual. INDIANA UNIVERSITY, BLOOMINGTON, APRIL 8, 1902. Explanation of Plate VI. Drawings by Sydney Prentice, except No. 12, which is by C. McK. Beede. All specimens natural size. _Seminula argentia._ Variation of spires. FIG. 1. Specimen brachial side up. FIG. 2. This specimen shows spires viewed with pedicle side partly removed. FIG. 3. Pedicle view, showing part of spire. FIG. 3_a_. Above individual, brachial side up. FIG. 4. Brachial side of fig. 4_a_. FIG. 4_a_. Pedicle view of specimen, showing position of spires. FIGS. 5 and 5_a_ are the brachial and pedicle views of a somewhat laterally compressed specimen. FIG. 6. Pedicle view of specimen. FIG. 6_a_. Brachial view of fig. 6. FIGS. 7 and 7_a_ are the brachial and pedicle views of a specimen. FIG. 8. This figure probably shows the brachial side of specimen, while fig. 8_a_ is the opposite side. FIG. 9. Brachial view. FIG. 10. The pedicle view of a specimen, and fig. 10_a_ the brachial side of the same.