190 DB. C. J. iOaSYTH iUJOK OX MIOCE^^E SliUlRHELS. [Jbeb. 2», 



" middle-sized " Oriental Squirrels. Divisiou y, mtli Sc. vnh/aris 

 and tSc. si/riacus, distinguished from each other by slight characters 

 of the first su])erior premolar (p^). Division ^ contains most of 

 the American Squirrels. 



The third subgenus c. is Tamlas, which 1 cannot separate from 

 the genus Sciunis. 



The skull of the Pigmy Squirrels is very remarkable, a fact to 

 which attention has been drawn by Midler and Schlegel, as well as 

 by 0. Thomas. The anterior zygomatic root is a perfectly vertical 

 nain'ow septum, and is placed so much backwards (above the second 

 molar) that the facial part of the cranium appears veiy elongate, 

 whilst the frontal region is broader relatively than in any other 

 Sciuromorpha. The orbita is formed by an almost circular bony 

 ring. 



The dentition, of which I give the figures (Plate X. fig. 10, 

 Plate XI. figs. 6, 7) is unique amongst Sciuromorpha, and can, as 

 I have said before, be compared only with that of some 2L/o.vi, 

 In the upper jaw there are either one or two premolars, and one 

 in the lower jaw. The posterior upper ])remolar (p') and the 

 lower premolar (p J are of minute size as compared to the homo- 

 logous teeth in other Sciuromorpha, sometimes scarcely one-third 

 of the size of the molars. This is another feature they have in 

 common with certain of the Miio.vi. The pattern of the crown 

 differs from that found in the Sciuromorpha generally, in pre- 

 senting only three complete transverse crests in the upper molars 

 instead of four, and three in the lower molars. The third crest, 

 counting from front to back", of Sciuromorphous molars is very 

 reduced in these pigmy Squirrels, sometiuies scarcely more than a 

 minute cusp. A further peculiarity of these molars is the large 

 development of the anterior transverse Aalley of both superior and 

 inferior molars, as compared to the usual Sciuromorphous type, 

 sometimes almost equalling that of the posterior valley. This last, 

 owing to the partial suppression of the third crest (Riitimeyer's 

 Nachjoch)^ occupies the area of the median as well as that of the 

 posterior trans\erse \alley in the tooth of Sciuromorpha. 



These characters of the teeth and the skull of the Pigmy 

 Squirrels sufficiently justify the creation of a separate subfamily for 

 them. 



IV. Desi.'1'iplion of the Fossil Sj^ecies. 



The remains of two species of Squirrels are representatives, the 

 one (1) tScinrus spermophtlinus, Dep.', of the Sciaras VHlgaris-tj\)e, 

 the other (2) Xeras (jrivi'ufiis, u. sp., of the A'f/'HS-type, which both 

 types have been so fully discussed before, that I ueed scarcely 

 enter into further details. 



' Oh. Deperet, " Eecherches 8ui' la succession des Faunes de Vertebres 

 miocenes de la Vallee du Rlione," Arch, dii Mus. d'Hist. Nat. de Lvon, t. v. 

 (Lyon, 1887), pp. 108-110, pi. xiii. figs. 14, 14a. 



Id., "La Faune de Mamniiieres miocenes de la Grive-Saint-Alban (Isere), etc.," 

 Arcli.Mus. d'Hist. Nat. de Lyon, t. v. (Lyon, 1892), pp. 48-00, pi. i. figs. 26-27. 



