. Bulletin of the Department of Geology of the University of California. 366 University of California. [Vol. Figure i.—Sigmogomphius Le Contei. a, Skull, seen from above (natural size). F, frontal; N, nasal; Pm, premaxillary; M, maxillary; I, incisor, b, right and left superior molar series (twice nat- ural size). Right premolar shown in section (heavy line) a short distance above the triturating surface. genus, it should perhaps be stated that, although the head bones extend backward beyond the molars, no sign of a fourth tooth could be found on either side. The striking resemblance of th
. Bulletin of the Department of Geology of the University of California. 366 University of California. [Vol. Figure i.—Sigmogomphius Le Contei. a, Skull, seen from above (natural size). F, frontal; N, nasal; Pm, premaxillary; M, maxillary; I, incisor, b, right and left superior molar series (twice nat- ural size). Right premolar shown in section (heavy line) a short distance above the triturating surface. genus, it should perhaps be stated that, although the head bones extend backward beyond the molars, no sign of a fourth tooth could be found on either side. The striking resemblance of the molars to those of Eucastor, Leidy, Fig. 2, a, which possibly possessed only three superior molar teeth, makes it appear the more probable that the fourth tooth was absent in Sigmogomphius. The molars were semi-hypselodont or semi-prismatic and strongly curved. They attained about half the size of those in Castor fiber, averaging near i mm. long; crowns, mm. transversely, mm. antero-poste- riorly. Evidently they were not rooted till late in life, beginning to close up on the outer posterior corners, at which place a small lateral root was formed, the main portion continuing to grow for some time after this separation. The crowns of the premolars were larger than those of the molars, being about one-fourth longer and broader. Molars one and two were of nearly equal size. The triturating sur- face of the premolars is nearly triangular in outline; that of the molars is more nearly quadrate. All are set obliquely in the jaw, so that the folds of the enamel wall do not cut the fore-and-aft axis of the tooth at right angles, but obliquely. The inner wall of all the molar teeth is thrown into a single strong fold, which, in the first tooth, traverses half the breadth of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble
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