;i:«) 
OX THE STRUCrUIiE AND CLASSIFICATION 
SrALACOTHERIUM, Owen,' 1854. 
, nm- mr The incisors are compactly placed, pointed and 
,ecur :: Tr»;:ine'i: Jhev;,e„aer.e.ect and necnn-ed. The pre.nohn, have 
„.erior '“ cingulum cusps” and prominent posterior “ basal cj. The mam cusp 
7{ the molarsl continuous upon its outer face with the rn cmal y placed antpor and 
,M»lerior cusps. The Internal cingulum forms a broad shelf. The angle and condyle 
are both elevated. 
I.eft lower jaw of Memicodon rarus, outer and inner view ; three tunes natural size. After 
MENACODON, Marsh, " 1887. 
DcntUion—iZ, cj, pin:,, m',. The canine is small and directed well forward. 
'Die premolars resemble those of Spalacotherium. The anterior and posterior cusps 
of the molars are not so fully rotated inwards as in the foregoing genus and are more 
separate u|)on the outer face. The median cusp is less lofty, 'fhe mylohyoid groove 
is less distinct. 
Noth. — An\}»hiti/hit< is placed in the Triconodontidce upon the Imsis of its molar 
structure, although the position of its condyle is exceptional and considered alone 
would nunovc it from this group. The position of the condyle in Amphilestes is 
inferred from Owen’s description and earlier figures (see Plate VIII, fig. 1). It will 
Ik* * observed that Juioiloti, in its molar structure and the shape of the jaw, aftbrds 
such a clear transition between the Amphilestincn and Spalacotheriinm, that there is 
no pr(‘.s('nt ground for a wider separation of these genera than that here adopted, 
although such ground may be subsequently discovered.* If the number of the 
premolars and molars be allowed great weight in classification it is clear that the 
almve genera must Ik; divided into four families. 
2. Omnivohous Skkiks. 
AMI'IIITHPAtllDA:, Owen/ 184(). 
Upper molars irith one main external cusp and two lateral cusps, and one main 
' "tjuart. Jour. (ieol. Soc.,” London, vol. 10, p. 426. 
• “Am. Jour. S<'. and Arts,” April, p, 340. I follow Professor Marsh’s description, although 1 think it 
not improbable that four premolars and five molars will be found in a more complete specimen. 
It is so easy to overlook the distinctions between the premolar and molar patterns in these minute 
jaws (sec .Marsh, Tincxtnn, p. 340, “Am. Jur. Mamm.”), that until the post-canine dentition of Tinodon is fully 
deerribed and ligureil I may be pardoned for questioning the statement that “the premolars of this genus 
have the same general form as the molars.” This statement is also made in regard to Mesacodon, in which the 
premolars arc very distinct in pattern from the molars (p. 340). 
‘ “ Rritisb Fossil.Mammals and Birds,” 1846, p. 29. 
