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Show 1893.] DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. 211 examination of the figures and descriptions without having seen the originals ; but I wish to offer a few remarks. Marsh has considered a certain number of isolated molars, possessing three longitudinal pairs of elevations, to be upper molars, although the type of Bipriodon robustus, the only molar which is undoubtedly from the upper jaw, left side, " its position being decided by a portion of the maxillary attached to it," ' apparently has only two longitudinal rows. This circumstance has given origin to part of Osborn's criticisms2. The type of Tripri-oclon coslatus3, considered by Marsh 4 as the first upper molar of the left side, as well as the type of Selenacodon fragilis5, also stated to be an upper molar (both having three longitudinal rows of cusps), are declared by Osborn to be respectively a last lower molar of Meniscoessus, and an anterior lower molar of the same6. In a subsequent note7 Osborn writes as follows :-" It remains for the author to show specifically that the types of Selenacodon and Tripriodon are maxillary teeth," adding: " I should myself have considered them as such but for the fact that the type of Bipriodon robustus, with two rows of tubercles, was described as a maxillary tooth, and figured with a supposed fragment of the zygomatic arch attached to the alveolar border." With regard to the upper molars, Marsh asserts, in his latest paper on the subject, that he has the means of showing what Osborn has objected to : " Although not found in position in any one specimen, so many have been secured with portions of the jaw attached, that their place in the dental series has been ascertained in several forms ;" and he goes on to state, " that the upper molar teeth may be separated into two series, the first having three longitudinal rows of elevations on the crown, and the second series but two rows "8. With the caution imposed by the fact that I am judging only from the published figures, I venture to suggest that the type of Bipriodon robustus, which has the undoubted fragment of the zygomatic arch attached to the alveolar border, had originally three longitudinal rows of cusps, the middle one being worn off. Marsh himself states that its " points are somewhat worn"9, and this appears to m e clearly shown iu his figure 10. If we now assume that where there are three rows of tubercles above and two below, " the cusps of the lower rows fit into the valleys of the upper teeth" " (which in my 1 Marsh, I. c. part I. p. 85, pi. ii. figs. 13-15. 2 As stated by Osborn himself in " A Reply to Professor O. C. Marsh's ' Note on Mesozoic Mammalia.' " Reprinted with slight alterations from the 'American Naturalist,' September 1891, p. 782. 3 Marsh, I. c. part I. pi. ii. figs. 19-21. 4 L. c. p. 86. 5 Marsh, I. c. part I. pi. ii. figs. 22-24, p. 86. 6 H. Fairfield Osborn, "A Review of the Cretaceous Mammalia" (Proc. Acad. Nat. Sc. Philadelphia, 1891, p. 128). 7 A Reply to Professor O. C. Marsh's Note, &c, p. 782. 8 Part III. p. 253. 9 Part I. p. 85. 10 i.e. pi. ii. figs. 13, 14. 11 Osborn, " A Review of the Cretaceous Mammalia." 14* |
