12 MARSUPIALIA. 
strongly developed, and divided longitudinally by a pro- 
minent ridge, the continuation of which forms the posterior 
edge of the body of the tooth. At the base of the anterior 
root of the tooth, the opening of a foramen is seen, on the 
outer surface of the bone.” 
In subsequently studying this fossil, I have not been 
so satisfied as to its unequivocal indication of the genus 
or family of the small zoophagous Mammal of which it 
formed part. There is no tooth so little characteristic, 
or upon which a determination of the genus could be less” 
safely founded, than one of the spurious molars of the 
smaller carnivorous and omnivorous Pere and Marsupialia. 
A large, laterally compressed, sharp-pomted middle cone, 
or cusp, with a small posterior and sometimes also a small 
anterior talon, more or less distinctly developed, is the 
form common to these teeth in many of the genera of the 
above orders. It is on this account, and because the tooth of 
the fossil in question differs in the shape of the middle, and 
in the size of the accessory cusps, from that of any known 
species of Didelphys, that I regard its reference to that 
genus as premature, and the affinities of the species to 
which it belongs as wanting further evidence, before they 
ran be determined beyond the reach of doubt. Besides 
the presence of the anterior tubercle, or talon, and the 
larger and more complicated posterior tubercle, the middle 
compressed cone is more equilateral and symmetrical than 
in the corresponding tooth of the Opossum. 
The crown of the premolars of the placental Mera, which 
present the same general form as the fossil, are thicker 
from side to side, im proportion to their breadth; the pre- 
molars of the Dasyurus, Thylacinus, and Phascogale, ditter 
in like manner from the fossil. It is in the marsupial 
genera Didelphys and Perameles that the false molars pre- 
