. Bulletin. Natural history. FIG. 16. Sagenodus. Skull roof in dorsal view. Reconstructions, showing different conditions of the dermal bone pattern. Redrawn from Westoll (1949) with new dermal bone notations. both the anterior and posterior pit lines in exactly the same arrangement as the Late Devonian genera Scaumenacia and Fleurantia. By Late Devonian times the lateral parts of the commissure had already migrated forward from H to I, and it is no surprise to find its median part moved forward to B. Z can still be recognized by the junction in it of the occipital commissure and the main late
. Bulletin. Natural history. FIG. 16. Sagenodus. Skull roof in dorsal view. Reconstructions, showing different conditions of the dermal bone pattern. Redrawn from Westoll (1949) with new dermal bone notations. both the anterior and posterior pit lines in exactly the same arrangement as the Late Devonian genera Scaumenacia and Fleurantia. By Late Devonian times the lateral parts of the commissure had already migrated forward from H to I, and it is no surprise to find its median part moved forward to B. Z can still be recognized by the junction in it of the occipital commissure and the main lateral line canal, but it, too, tends to be wedged in between the Y series and I, thus carrying the commissure farther forward. The elements Yv Y2, X, J, 4, and 3, can all be recognized by the same criteria as those for Devonian genera. In Westoll's restora- tion (1949, fig. 8A-A') there seems to be evidence from shape (particularly the notch for the articulation of the operculum and the position of the lateral-line canal- anterior pit-line junction), for the fusion of X and Yt in some specimens (Fig. 16B). However, Watson and Gill (1923, fig. 1, 2, and 6) show that these bones have a single center of radiation; therefore a more reasonable interpretation is that the space occupied by Yx has been captured by X. The fact that X and Y1 exist independently on one side of some specimens does not affect this argument one way or the other. The position of the palatoquadrate is not known, but we would suspect that, with the incorporation of Z into the fixed series of roof bones, the quadrate ramus would be in contact with Y2 and Z. We regard K as absent for reasons given in the discussion on Scaumenacia. The bone that lies between ]1 and 3 on the left side of Westoll's figure 8A' must be Lx (Fig. 16B). Judging from the radial pattern shown by Watson and Gill on the bones Westoll labels M + L2 + K, we conclude that L2 has captured the space that in Scaumenacia is occupied by L1( L2, and M.
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