1893.] DR. C. J". FORSYTH MAJOR ON MIOCENE SQUIRRELS. 213 



of Sardinia \ and to a subsequent paper by myself on the same 

 subject ^. 



Marsh has recently made the followinoj statement : — " One fact is 

 becoming more and more evident, the near affinity of the early 

 Primates, Carnivores, Ungulates, and Rodents, with each other 

 and with the Insectivores, and more remotely with Marsupials. 

 The key to the mystery lies concealed in the great break between 

 the Lower Wahsatch, at the base of the Eocene as now known, and 

 the Laramie beds of the Cretaceous. In the latter, none of the 

 above placental mammals have been found, but in the early Eocene 

 occur, side by side, Carnivores, Eodents, and Ungulates . . ." ^ 



I have endeavoured to show that the key to the mystery actually 

 lies for the chief part in Prof. Marsh's own hand, and I Irust that he 

 himself will before long furnish us with the full proofs that several 

 at least of the Cretaceous AUotheria, so called, are hi the direct 

 ancestral line of Eutheria. 



And, in the meanwhile, I confidently state as follows my 

 conclusions as to the priaiitive type of the Eutherian molar: — 



(1) The primitive condition of the Eutherian molar is that of 

 polybu ay. 



(2) The single tubercles or cusps were arranged in longitudinal 

 series {Tinotaxis), divided by lougitudinal grooves or valleys, there 

 being generally three rows with two grooves in the upper, and two 

 rows with one groove in the lower molars. 



(3) Microlestes may prove to be a remote ancestor of the 

 Eutheria. 



^ R. Hensel, "Beitriige zur Kenntniss fossiler Saugethiere. — II. Ueberreste 

 von Miis in der Breccie von Cagliari," Zeitsclir. d. deutsch. geolog. Gesellschaft, 

 viii. Band, 1856, p. 281. The conformation of the first upper molar of Mus 

 is described by Hensel as follows : — " Seine Krone zerfiillt durcli zwei fast bis 

 aiif den Grund der Krone eindringende Querfurchen in drei Querleisten, von 

 welc'hen die beiden ersten naeli vorn convex, nach hinten zu concav erscheinen . . . 

 Zwei verhaltnissnuissig seiclite Langsfurchen zertheilen wiederum jede Quer- 

 leiste in drei mebr oder weniger deutliclie Hocker . . . Das Schema fiir die Back- 

 euziihne des Unterkiefers (Fig. llh) ist ein wesenllieh anderes. Zwar sind 

 auch bier die Kronen dtn-ch zwei Querfurchen iu drei Querleisten getheilt. 

 AUein statt zweier Langsfurchen findet sioh nur eine, so dass jede Qiierleiste in 

 zwei Hocker, die ganze Zahnkrone also in sechs derselben zerfiillf." {L. c. p. 282.) 



^ Forsytli Major, " Sulla confornuizione dei Molari nel Genere Mhs, e sul 

 M^is meridinnnllse Mus orfhodnn, Hensel," Atti Soc. Tosc. Sc. Nat. Proc. Verb. 

 1888, pp. 129-14r). — Mr. Oidfield Thomas has lately drawn my attention to his 

 " Description of a new Genus and Species of Rat from New Guinea," the Chiru- 

 romi/s forhe.si (Proc. Zool. Soc, April 17, ISSS, pp. 237- 2-10, fig. 2, p. 239). In 

 this paper it is stated that the teeth of Chiruromys "are remarkably compli- 

 cated, and sliow a high degree of specialization, far more tiian is found in any 

 other genus at all allied to the present one," and that "tiiis extreme speciali- 

 zation both of teeth and tail is especially remarkable iu an animal inhabiting 

 such a refuge for old and litMe-modified forms as New Guinea." From what I 

 have been saying, it is to be inferred, that the teeth in qnesti(m, far from 

 showing a high degree of specialization, are, on tlio contrary, of a very 

 generalized typo, precisely such as we might ai'licijiato to meet with in a refuge 

 for old and little-modified forms. 



•' O. C Mar.sii, '■ A new Order of extinct Eocene Mammals (Mesodactyla)," in 

 American Journal of Science, vol. xlii. May, 18'J2, p. 44*.), 



