254 
(4N THE STRUCTUKE AND CLASSIFICATION 
IV— the zoological position of the MESOZOIC MAMMALIA. 
A. FIRST GROUP. 
While the Multituberculata are widely separated from the mammals of the 
second group, they are so closely related to each other by the unique structural and 
functional adaptations of the dentition, that the discovery in one genus of a single 
ta.xonomic character, which is distinctive, will probably determine their position either 
with the Monotremata or Marsupialia or in an independent order ; no character of 
such importance is known at present. Their relation to the Marmpialia was proposed 
by Falconer*, accepted by Owen^ Cope® and Marshy and in fact has not been ques- 
tioned until Poulton’s® recent discovery of multitubercular teeth in Ornithorhyn- 
chtUy which has led Cope to suggest their reference to the Monotremata.® 
Falconer and Owen referred Plagiaulax to the Diprotodontia, principally on the 
following grounds: the similarity of the premolars and incisors to those of Hypsiprym- 
niM, and the slight inflection of the lower inner margin of the ramus. Cope sepa- 
mtcd the MultitulKTculata as a sub-order from the Diprotodontia, but gave additional 
grounds for their reference to the Marsupialia, from his observations upon the skele- 
ton of Pofyma«fo(lon, as follows: the inflection of the angle of the jaw and the 
jiosition of the dental foramen at the apex of the masseteric fossa; the astragalus is 
without trochlea and bears a large facet for the cuboid bone, with a narrow hLd and 
navicular face convex in a vertical direction only, a form much like that of Ilahna- 
inrm. The condyle of the humerus has a double articular facet, and a stron<^ and 
tliick inlcrtrocl.lonr ridge in front. The distal end of the humerus of 
.lK|.lnp the some cimracters. In the skull of D-ili/lodon, we observe the marsupial 
nffimties ,n the terminal imsition of the anterior nares, in the junction of malars and 
lachrymals and the exclusion of the premaxillaries from the frontals 
-Ote writer has provisionally adopted Cope’s sub-order in this memoir.’ Ly- 
deseribedthis group as primitive Diprotodoni;. 
nnW r n "I ’ / -evidence for general mar- 
suldv or e 1 Iv" -cond,?hat a close 
special ml«tiortL'thrnrp“r''' their supposed 
M rv, Plagiaulax, &c.’> 
MomoirB. \ ol. II, p. 43 i». 
Mfsotoic Mammalia,” p. S8. 
Maraupialia,” Am. Nat., 1884, p. 688. 
‘ “American JuraPsic Mammals,” loc. cit., p. 345. 
^ ^y. .Soc. Pr<K'6e<linpi, Febniary, 1888. 
‘American Naturalist.” March, 1888, p. 259. 
I nhil&« Acft<I .TiinA iftQ7 A I A 
• Cat. Foes. .Mamm.,’ Part V, p. iog Naturalist, March, 1888, p. 232. This Memoir p. 213. 
Quart. Journ. Geol. Soc., August. 1857. Palseontol, 
Also, “Tertiary Vertebrata,” Hayden’s Surv., 1884, 
