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Show 1897.] MALAGASY GENUS BRACHYUROMYS. 705 In the Anthracotherina, e. g. in Ancodus ', and in the Ancylopoda we find three widely bulging cusps in the upper molars. In Hyracotheria 3 it is easy to see that the two posterior of the three outer cusps have nothing whatever to do with the two posterior of Ancodus and the Ancylopoda ; only their anterior one, which I consider as homologous with cusp 1 of Insectivora and Dldelphys, is the homologue of the anterior cusp in Hyracotheria. The two posterior cusps of Ancodus and the Ancylopoda are 2 and 3 ; those of the Hyracotheria are the homologues of the two cusps more internally situated iu the former, Winge's 4 and 5, Osborn's paracone and metacone ; the comparison with other Hyracotheria 4, in which something more of these " -styles " is preserved, shows this at once to be the case. The posterior outer cusp in upper molars, Winge's 3, Osborn's metastyle, which is so well developed in Dldelphys and in many Insectivora % is, when met with at all in other orders, generally the least developed of the three outer cusps, and there is sometimes a relation in its development with that of the antero-internal cusp in lower molars, Winge's 1, Osborn's paraconid. The fact, pointed out by Winge, that these cusps of Insectivora and Didelphyinae have their homologues in other orders, chiefly in the older members, is of the greatest importance and a notable progress in our knowledge of the homologies of the Mammalian molar. It is a very remarkable fact, that this outermost series of cusps is enormously developed in several upper molars from the Laramie Cretaceous 6. Whether we have to consider them, with Winge, as being the most primitive parts of the molar, older than the cusps situated internally from them in upper, externally in lower molars, is quite another question, in which it is not proposed to enter particularly for the present. As regards the Eodents, Winge points out the remnants of this 1 Cf., e.g., Zittel, ' Handbuch d. Palaontologie,' iv. p. 329, fig. 266. 2 Zittel, /. c. p. 314, fig. 255. 3 J. L. Wortmann, " Species of Hyracotherium and allied Perissodactyles from the Wahsatch and Wind River Beds of North America," A m . Mus. Nat. Hist. vol. viii., vi. 1896, p. 89, fig. 3, p. 95, fig. 4; Zittel, I. c. p. 277, fig. 219. 4 Zittel, I. c. p. 243, fig. 179, p. 242, fig. 171 (Pachynolophus siderolithicus); Wortmann, I. c. p. 108, fig. 18 (Orcohippus). 5 Winge, /. c. pl. iii. fig. 1 b, 2 b, 3 b. 6 Cf. H. F. Osborn, "Fossil Mammals of the Upper Cretaceous Beds," Am. Mus. Nat. Hist. vol. v. Art. xvii. pl. viii., N e w York, 1893. Osborn calls the molars referred to " trituberculates," and expresses his belief that they lend " overwhelming proof, if any more were needed, of the unity of origin of the molar types of tbe higher Mammalia from a tritubercular stem instead of from a multitubercular, as Forsyth Major has suggested'' (I. c. p. 320). For me these Laramie " Trituberculates," so-called, are polybunous, as well as those figured on pl. vii.; and I have only to repeat once more that " trituberculate " and " triangular" are not synonymous. Prof. Osborn assures us (/. c. p. 320) that these "Laramie Trituberculates" "include a variety of forms just emerging from the primitive tritubercular stage." That is precisely what has yet to be proved. But even if we were inclined to take Prof. Osborn's assertion for granted, it would have to be shown how it happens that several of these ancient forms (E, F, pl. viii.) have in their yery process of " emerging " already acquired such a luxury of "-styles "and "-conules," as to constitute by themselves alone half of the molar's crown. |
