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Show 1893.] DR. C J. EORSYTH MAJOR ON MIOCENE SQUIRRELS. 185 shape of inferior molars tends to disappear. The species which present in a greater or lesser degree this conformation are, besides Xerus (Plates VIII. and IX. fig. 10), including X. getulus, Gesn. (Plates VIII. and IX. fig. 9), Sc. palliatus, Pet., Sc. cepapi, Smith (Plate VIII. fig. 22, Plate IX. fig. 23), So. pyrropus, F. Cuv. (Plate VIII. figs. 15, 23, Plate IX. figs. 15,22),$?. eongicus, Kuhl, Sc. lemniscatvs, Le Conte, Sc. Isabella, Gr. (Plates VIII. and IX. fig. 24), and Sc. boehmi, Reich. At the same time they present in their skull some resemblance to the Hystricomorpha. They also approach Anomalvrus (Plates VIII. and IX. figs. 13, 14), the various hystricomorphine characters of which have long ago been noted, but have, I think, rather been underrated by Alston1. It thus would appear that we have here a group of Sciuromorpha, somewhat specialized in the direction of Hystricomorpha, as we find, too, in several Eocene Rodentia. But this is not all. The molars of Se. berdmorei, Bly. (Plates VIII. and IX. figs. 16-18), an Oriental Squirrel, and those of the Bornean " Rhinosciurus, Gr." (Plates VIII. and IX. figs. 11, 12), agree with those of Xerus and the above-named Ethiopian Squirrels, not only in their semi-hypsodontism, but likewise in their lopho-dontism, whilst the less semi-hypsodont Oriental Sc. tristriatvs, Waterh., and Sc.palmarum, L., tend to connect the Zmts-type with the Sc.-vulgaris-type, in approaching the form of molar of most of the "middle-sized" Oriental Squirrels. Two other Oriental species, Sc. insignis, F. Cuv. (Plates VIII. and IX. fig. 6), and Sc. hosei, Thos.2 (Plates VIII. and IX. fig. 5), from Borneo, though semi-hypsodont, and in other characters agreeing with the members of the Xerus-growp, show a remarkable modification in the pattern of the molars, the valleys being reduced to mere superficial cracks, which disappear very early by wear. I think that we have in the molars of these two forms examples of that kind of retrogressive evolution of the molars to which attention has been lately drawn in an important paper by Leche 3, w ho attributes it to the modification of food. The Macroglossi, Pteropus scapulatus, and the Epomophori, differing in this respect from other Pteropi, feed on juicy fruits, wrhose contents need not be chewed. Likewise Chiromys madagascariensis, the molars of which present a similar kind of retrogressive evolution, is known to feed principally on succulent juices, especially of the sugarcane, as well as on wood-boring caterpillars. It now is very suggestive that Sciurus insignis, according to Miiller and Sehlegel \ is especially fond of juicy and aromatic fruits of different species 1 Edward R. Alston, " On Anomalurus, its structure and position " (Proc. Zool. Soc. 1875, p. 94). 2 Ann. Mag. Nat, Hist, for Sept. 1892, pp. 215, 210. 3 W . Leche, " Studien iiber die Entwicklung des Zahnsystems bei den Saugethieren," Morpholog. Jahrbuch, xix. 1892, pp. 543, 544. 1 Sal. Miiller & Herm. Sehlegel, " Over de tot heden bekende Eekhorens (Sciurus) van den Indischen Archipel," Verhandeliugen over de Naturlijke Geschiedenis der Nederlandsche overzeesche Bezittingen," Leiden, 1839-44, p. 99. |