1893.] DE. C. J. FOESXTH MAJOR OTS MIOCEIfE SQUIRRELS. 213 



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

 subject ^. 



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

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

 Primates, Carnivores, Ungulates, and Eodents, 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 L^ngulates . . .'" ^ 



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 trust that he 

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

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

 ancestral line of Eutheria. 



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

 conclusious as to the primitive type of the Eutherian molar: — 



(1) The primitive condition of the Euthei'ian molar is that of 

 polybu ny. 



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

 series (Tinotacvis), divided by longitudinal 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 proxe to be a remote ancestor of the 

 Eutheria. 



* R. Hensel, " Beitrage zur Kenntniss fossiler Saugethiere. — II. Ueberreste 

 von Miis in der Breccie vou Cagliari," Zeitschr. d. deutsch. geolog. Gresellschaft, 

 viii. Band, 1856, p. 281. Tlie conformation of the flr.«t upper molar of 3fus 

 is described bv Hensel as follows : — " Seine Krone zerfallt durch zwei fast bis 

 auf den Grund der Krone eiiidringende Querfurchen in drei Querleisten, von 

 weiehen die beiden erst«n nach vorn convex, nach hinten zu concav erscheinen . . . 

 Zwei verhiiltnissniassig seichte Langsfurchen zertheilen wiederum jede Quer- 

 leiste in drei mehr oder weniger deutliche Hocker . . . Das Schema f iir die Back- 

 euziihne des Unterkiefers (Fig. Hi) ist ein wesentlich anderes. Zwar sind 

 aueh bier die Kronen durch zwei Querrurchen in drei Querleisten getheilt. 

 AUein statt zweier Langsfurchen findet sieh nur eine, so dass jede Querleiste in 

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



^ Forsyth Major, "Sulla conforniazione dei Molari nel Genere Mus, e sul 

 Mils meridinnaUs e Mus orfhodon, Hensel," Atti Soc. Tosc. Sc. Nat. Proo. Verb. 

 1888, pp. 129-14.5. — Mr. OldOeld Thomas has lately drawn my attention to his 

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

 ro7nysforbesi (Proc. Zool. Soc, April 17, 1888, pp. 237-2-10, fig. 2, p. 239). In 

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

 cated, and show a hifrh degree of specialization, far more than is found in any 

 other genus at aU allied to the present one," and that "this extreme speciali- 

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

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

 have been saying, it is to be inferred, that the teeth in question, far from 

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

 generalized type, prec-isely such as we might anticipate to meet with in a refuge 

 for old and little-modified forms. 



^ O. C. Marsh, " Anew Order of extinct Eocene Mammals (Mesodactyla)," in 

 American Journal of Science, vol. xlii. May, 1892, p. 449. 



