OCR Text |
Show 1893.] DR. C J. EORSYTH MAJOR ON MIOCENE SQUIRRELS. 181 cumstance is of no small importance, as I shall have to point out later on. The Common Squirrel, and many Oriental members of the genus, as well as some Ethiopian Squirrels (Sc. rufobrachiatus, Waterh., annulatus, Desm., shirensis, Gray, punctatus, Temm.), show relatively prominent cusps, and present a transitional stage between semi-hypsodontism and brachydontism. Still more brachydont are two other groups which have little affinity with each other-the African Sc. stangeri, Waterh., Sc. elni, Temm., Sc. aubinnii, Gr., the Oriental Giant Squirrels (Sc. bicolor, indicus, macrurus, &c). The Oriental Pigmv Squirrels (Sc. exilis, Miill., Sc. melanotic, Mull. & Schl., Sc, concinnus, Thos. (Plate X. fig. 10, Plate X L fig. 7), Sc. whiteheads, Thos.), as well as the pigmy Ethiopian Sc. minutus, D u Chaillu (Plate XI. fig. 6), show a low, oval-shaped and nearly horizontal crown, slightly concave in the middle, with transverse ridges. On the whole, their dentition has scarcely anything to do with the Sciuromorphous type of molars, and can only be compared with that of the Myoxida?, Eliomys and Graphiurus. Next we have to consider the pattern of the molars in Sciurinee. The numerous modifications-almost every species presents some peculiarity-may be arranged under three heads:- 1. The first type is represented by the most brachydont forms: some Eocene Squirrels, as Sc. spectabilis, Maj., from Egerkiugen, the Bornean Rhithrosciurus (Plate IX. fig. 2), the Oriental Giant Squirrels (Plates Till, and IX. fig. 1), the Ethiopian Sc. stangeri (Plate Y H I . fig. 7, Plate IX. fig. 7) and its allies, Sc. ebii and Sc. aubinnii (Plates Y H I . and IX. fig. 8). 2. The second type is represented by Sc. vulgaris and its ally Sc. syriacus (I have had no opportunity of examining the dentition of the Japanese Sc. lis), by most of the Oriental middle-sized Squirrels (Sc. prevosti (Plate Y H I . fig. 2), Sc. lokroides (Plates VIII. and IX. fig. 3), & c ) , by a small Ethiopian group (Sc. shirensis, Sc. annulatus, Sc. punctatus, Sc. rufobrachiatus), and most of the American Squirrels. 3. The third type is represented by several groups of Ethiopian Squirrels: Xerus (Plates Y H I . and IX. fig. 10), including the Moroccan X.getulus (Plates Y H I . and IX. fig. 9), by Sc. cepapi (Plate Y H I . fig. 22, Plate IX. fig. 23), Sc. palliatus, Sc. pyrropus (Plate VIII. figs. 15, 23, Plate IX. figs. 15, 22), Sc. congicus, Sc. lemniscatus, Sc. isabella (Plates VIII. and IX. fig. 24), Sc. boehmii; as well as by some Oriental forms, Sc. berdmorei (Plates VIII. and IX. figs. 16-18), Gray's genus Rhinosciurus (Plates VIII. and IX. figs. 11, 12), &c. I do not consider for the present the African and Oriental Pigmy Squirrels, as the characters of their dentition depart entirely from the Sciuromorphan type as a whole. Brachydontism in itself is quite generally admitted to be the most generalized condition, and the teeth point iu the same direction as do those of other Orders, viz., towards a still more primitive type. Besides, we are able to show that the two other |