ox tiik structure and classification 
ft.atures and of their ancestral position, these mammals may be distinguished from 
the recent Marsuihals as tlie sul>order Prodidelphia. 
Relations to the Insectivora. 
It has been shown that the Stylacodontidm have the dentition and jaw peculiarly 
adapted to an insectivorous diet (p. 235). They apparently present the tnhercuJar. 
sectorial molar pattern, a much more recent type than that attained in any other 
family. The nearest point of contact of this pattern is with Spalaeothenum, a genus 
widely separated from this family by its functional adaptation. The reduction of the 
prennilars and molars differs from that observed in other families (p. 248). The 
dentition is unifpie in combining the rapid progression of the molar pattern with the 
conservative retention of the primitive formula. All these facts go to support the 
a-ssumption that this family is on a distinct line of descent and that it separated from 
the line of the Trk-otiodontidcB, the only family to which in its molar pattern it is in 
any degree allied, at a very distant period. This is in the nature of demonstration 
that the marsupial affinity of Triconodon does not necessarily affect the position of the 
Styhu-odontUla;. Again, omitting the tubercular-sectorial molar which leads into 
both the marsupial and placental series, there is not a single marsupial characteristic 
in the dentition or mandible of this fuiiiily. Nor does any fossil or recent Marsupial 
prewmt tritulicrcular molars of the Stylacodon type. 
'I'he rc.scarches of 1 luxlcy,* Parker,^ Cope and others all point to the early origin 
and centnd {wsition of the Insectivora. We have abundant anatomical and embryo- 
logical evidence for the hypothesis of a primitive point of contact of this order with 
the Marsupials, to which additional palaeontological evidence can now be brought 
forward. 
-\mong the Insectivora we find traces of the primitive mammalian dentition in 
the retention of the simple tritubercular type and frequent occurrence of the bifanged 
c’anine, as in Ceatetes, Talpa and Oymnura. Some of the specializations of this den- 
tition have been enumerated recently in Schlosser’s exhaustive memoir.® These are, the 
chis<d-shaped incisors and elongation of the central pair; the occasional metamorphosis 
of the amine into an incisor as seen in Talpa ; the enlargement and complication of the 
posterior preraolars, beginning with the last and extending forwards; the reduction of 
* Op. cit., p. (167. 
‘he Skull in the Mammalia, Part III, Insectivora.” Phil, 
knowledira of iho Htr, ( ’ \ *i ‘he pre.<ent fragmentary 
(ype arc immo,iiaUOrarvr "tlie mIX'^'i? aX^thlt Th ' 
modifications of what is characteristic oT the Marsupwt > I«®ee‘ivora are more or less transformed 
