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Show 19b' DR. C. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. [Feb. 28, V. On the primitive Type of the Sciurine Molar, and of the Eutherian Molar in general. In surveying the various modifications of the Sciurine molar-type, I refrained from entering into the question as to their relation to the prevailing theory of trituberculism. I proceed now to this last part of m y paper. The tritubercular theory has been worked out with admirable acumen by Cope, Osboru, Schlosser, and lastly by Riitimeyer and Scott, and is so well known that I need not even give a summary of it. However, as 1 have to refer in the sequel to some less recent papers bearing on the argument, I may be allowed to mention them here as briefly as possible. In a Memoir, which may be regarded to contain the foundations of a real comparative Odontography, Riitimeyer was led to consider as fundamental type of the Ungulate molar the zygodont form, viz. the upper molars formed by two transverse ridges, parting under right angles from an outer wall (" Aussenwand"), with a transverse valley dividing them, and two simple transverse ridges in the lower molars1. fra Lagoa Santa, Minas Geraes, Brasilien. M e d Udsigt over Gnavernes ind-byrtes Slaegtskab" (Aftryk af " E Museo Lundii," Kjobenhavn, 1887). I regret not to have known this important publication before, but shall be obliged to take it into full consideration on the first opportunity if I succeed in overcoming the difficulties presented by the language. Meanwhile, at the risk of not having in every instance completely grasped the author's meaning, I cannot refrain here from a few observations. Winge presents (p. 110) the following genealogical tree of the Rodentia:- Myoxidaj. Murida'. \ / Dipodidae. Hystricidae. SaceomyicUe. \ / I Anoiualuridas. Sciuridas. \ . / Haplodontidse. Ischyromyidse. Leporida;. Pseudosciurus and Sciuroides are included as a distinct subfamily under the Anomalurida?, which last contain, moreover, besides Anomalurus (subf. Anoma-lurini), the Tertiary Trcchomys (Trcchomyini), Theridomys, Issiodoromys, Ar-chceomys (Theridomyini), and the recent Pcdetes (Pcdctini). I do not in tbe least deny the importance assigned to the masseter (in its relation to the mechanical action of the teeth), and, as a consequence, to the shape of the infraorbital foramen. However, the agreement in the molars of Sciuroides with those of Sciuropterus horsfieldi on the one side, and of Pseudosciunts with those of Sciuropterus pearsoni (and to a lesser extent of Allomys) on the other, is such that I do not think it justified to separate so widely these fossil forms from the Pteromyines. Besides, amongst Sciurinee proper, Protoxerus, ruy first subgenus of Xerus, still presents, in the conformation of the infraorbital foramen, some approach to the primitive condition. ' L. Riitimeyer, "Beitrage zur Kenntniss der fossilen Pferde und zur ver-gleichenden Odontographie der Hufthiere iiberhaupt," Verh. d. naturf. Ges. in Basel, iii. 1863, p. 558, gg. |