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Show 1893.] DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. 213 of Sardinial, and to a subsequent paper by myself on the same subject2. Marsh has recently made the following statement:-" One fact is becoming more and more evident, the near affinity of the early Primates, Carnivores, Ungulates, and Rodents, with each other and with the Insectivores, and more remotely with Marsupials. The key to the mystery lies concealed in the great break between the Lower Wahsatch, at the base of the Eocene as n o w known, and the Laramie beds of the Cretaceous. In the latter, none of the above placental mammals have been found, but in the early Eocene occur, side by side, Carnivores, Rodents, and Ungulates . .."3 I have endeavoured to show that the key to the mystery actually lies for the chief part in Prof. Marsh's own hand, and I trust that he himself will before long furnish us with the full proofs that several at least of the Cretaceous Allotheria, so called, are in the direct ancestral line of Eutheria. And, in the meanwhile, I confidently state as follows my conclusions as to the primitive type of the Eutherian molar:- (1) The primitive condition of the Eutherian molar is that of polybuny. (2) The single tubercles or cusps were arranged in longitudinal series (Tinotaxis), divided by longitudinal grooves or valleys, there being generally three rows with two grooves in the upper, and two rows with one groove in the lower molars. (3) Microlestes may prove to be a remote ancestor of the Eutheria. 1 R. Hensel, "Beitrage zur Kenntniss fossiler Saugethiere.-II. Ueberreste von Mus in der Breccie von Cagliari," Zeitschr. d. deutsch. geolog. Gesellschaft, viii. Band, 1856, p. 281. The conformation of the first upper molar of Mus is described by Hensel as follows :-" Seine Krone zerfallt durch zwei fast bis auf den Grund der Krone eindringende Querfurchen in drei Querleisten, von welchen die beiden ersten nach vorn convex, nach hinten zu concav erscheinen ... Zwei verhaltnissniassig seichte Langsfurchen zertheilen wiederum jede Quer-leiste in drei mehr oder weniger deutliche Hocker ... Das Schema fur die Back-euzahne des Lnterkiefers (Fig. 116) ist ein wesentlich anderes. Zwar sind auch bier die Kronen durch zwei Querfurchen in drei Querleisten getheilt. Allein statt zweier Langsfurchen findet sich nur eine, so dass jede Querleiste in zwei Hocker, dieganze Zahnkrone also in sechs derselben zerfallt." (L. c. p. 282.) 2 Forsyth Major, " Sulla conformazione dei Molari nel Genere Mus, e sul Mus meridionalis e Mus orthodon, Hensel," Atti Soc. Tosc. Sc. Nat. Proc. Verb. 1888, pp. 129-145.-Mr. Oldfield Thomas has lately drawn m y attention to his " Description of a new Genus and Species of Rat from N e w Guinea," the Chiru-romysforbesi (Proc. Zool. Soc, April 17, 1888, pp. 237-240, fig. 2, p. 239). In this paper it is stated that the teeth of Chiruromys "are remarkably complicated, and show a high degree of specialization, far more than is found in any other genus at all allied to the present one," and that "this extreme specialization both of teeth and tail is especially remarkable in an animal inhabiting such a refuge for old and little-modified forms as N e w Guinea." From what I have been saying, it is to be inferred, that the teeth in question, far from showing a high degree of specialization, are, on the contrary, of a very generalized type, precisely such as we might anticipate to meet with in a refuge for old and little-modified forms. 3 0. C. Marsh, " A new Order of extinct Eocene Mammals (Mesodactyla)," in American Journal of Science, vol. xiii. May, 1892, p. 449. |