704 DE. c. I. roESTTK MAJOR OH THB [June 1, 



Brack i/uromijs, and even less than in some oE the Bhizovii/s 

 (especially with i-en;ard to the lower molars). In the shape of the 

 outer wail of the infraorbital canal, Siphnms shows closer agree- 

 ment with Tachjorifcfes (especially with T. splendens) than with 

 Cricetus, the lower portion of the outer wall advancing more 

 forward. There is likewise more similarity than with Cricetus 

 in the form of the canal itself, which in TucJujoryctes and 

 Siphneus is broader in its upper part than in the first-named 

 genus, whereas (apparently as a consequence of the broadening of 

 the skull) in both the inferior, narrower part appears considerably 

 shortened vertically. In this respect Tacliyoryctes is somewhat 

 intermediate between Cricetus and Siphneus. The malar bone of 

 Siphneus is stronger than in Cricetus; in S. annancU it is as 

 strongly developed and reaches nearer to the iaehrymal than in 

 Tachyoryctes. As regards the flattening and inclination of the 

 occiput, there are different gradations in this respect in the genera 

 under consideration (Spalax, Siphneus, Ehizomys, Tachyoryctes) ; 

 one end of the series is occupied by Spalax. the other by 

 Tachyoryctes. In the latter the inclination is scarcely more than 

 in Cricetus frumentarius ; in old individuals scarcely less than in 

 young Spalax. 



For the rest the skull of Siphneus is transformed to be used as 

 a shovel and drill in a similar way as in Spalax. 



Tlie Molars of Brachyiiromys as compared with those of other 

 Muriclce and of Mammalia generally. 



A few introductory remarks are indispensable. 



In Didelphyidfe and many Insectivora there are on the outer 

 side of the upper and on the inner side of the lower molars three 

 very conspicuous cusps. These are considered by Winge'to be 

 the oldest, most primitive parts of the Mammalian molar. They 

 are the same which Osborn in upper molars has called 'parastyle, 

 mesostyle, metastyle ^ ; in Winge's plates " they are designated from 

 before backwards by 1, 2, 3. The middle one is supposed to be 

 the oldest of the three, so that according to Winge's view the 

 protocone is something toto coslo different from Cope's and 

 Osborn's protocone ; this last, 6 in Winge's figures, is according 

 to the latter author one of the latest additions to the tooth. 



If we review the more primitive Ungulates and the Ancylopoda, 

 we find equally three outer cusps in the superior molars ; but it 

 may be seen at once — and in this I think I am in agreement with 

 Winge — that they are not homologous in the different groups. 



^ H. Winge, " Om Pattedjreues Tandskifte, isser med Hensyn til Tasndprnes 

 Former." Vidensk. Meddel. Naturh. Foren. i. Kjobenhavn, 1882, p. 15, pi. iii. 



^ See e.ff. H. F. Osborn, "The Kise of the Mammalia in North America," 

 Address, Boston, 1893. p. 35 (text-figure of Anchitheriuni). H. F. Osborn and 

 C. Earle, "Fossil Mammals of the Puerco Beds," Ann. Mus. Nat. Hist, 

 vol. vii. Art. i., New York, 1895, p. 44, fig. 14. 



' L. r. pi. iii. H. Winge, " Jordfimdne og nulevende Pungdyr (Marsupialia) 

 fra Lagoa Santa, Minas Geracs, Brasilien. Med Udsigt over Pungdyrenes 

 Slfegtskab" ('"E Musoo Luiidii"), KjobenhavD, 1803, pi. ii. figs. 2a, 26, 

 8 6,10. 



