14 FOSSIL MAMxVIALIA OF THE 



is very characteristic of the mammalian nature of the bone ; it is long, narrow, and con- 

 tinued forward in the same line with the gently convex inferior margin of the jaw, 

 precisely as in Bidelphys, as well as in some other Ferines of both the marsupial 

 and placental series ; its lower margin presents a small notch corresponding with that 

 in the symphysis of the jaw in Myrmecohius. A greater proportion of the convex articular 

 condyle {h) is preserved in this than in the preceding specimen ; sufficient of the coronoid 

 remains to show that it had the same size and shape as that process in the type specimen. 

 A groove [g) is continued from below the dental canal {d), gradually contracting to a point 

 at the middle of the ramus. There is a broader and shorter groove in the corresponding 

 part of the jaw in the Myrmecohius, and a narrower groove in that of the SarcopJiilus 

 ursinus. The posterior molar shows a small middle internal and part of a larger 

 external cusp ; the premolars (4 and 5) are entire, and show the principal and posterior 

 basal cusp, as in fig. 21. The sockets of the missing teeth give not less than sixteen 

 teeth in each ramus of the jaw, viz. three incisors and one canine, each with a simple 

 socket ; six premolars and six true molars, each with a double socket. 



Thus, Amphitkerium was seen to differ from Didelphys even more than was inferred 

 from the evidence possessed by Cuvier. The only known existing Mammal with a 

 dentition approaching to the above is the Marsupial Myrmecohius (fig. 24), peculiar to 

 Australia. It has i 3 — 3, c 1 — 1, p 4 — 4, m 5 — 5 = 13 teeth, in each ramus. The 

 incisors are conical, separated at their base, the first the largest ; the premolars have 

 compressed conical crowns with a hinder talon ; the molars are relatively smaller than in 

 AmpJdtherium, and of the type of those of Microlestes. 



The additional evidence, from the second jaw, strengthens the inference from the first, 

 viz. that the Amphitkerium was a true warm-blooded Mammiferous species, unguiculate 

 and insectivorous, with a probability of its being marsupial. 



The third jaw in the order of discovery of Amphitherian fossils (PI. I, fig. 23, 23 a) is the 

 most complete one, containing the whole series of molar teeth, the last six being quinque- 

 cuspidate ; the first six unicuspidate, with basal cusps either on one or both sides ; it also 

 displays the socket of one small canine (c) and three longish slender incisors {i) in situ, 

 altogether amounting to sixteen teeth on each side of the mandible, as was indicated by 

 the sockets of the second specimen above described. 



This specimen is the right mandibular ramus presenting the outer side to view. The 

 convex condyle, the broad and high coronoid process, the backwardly projecting angle, 

 the lower margin of which bends slightly inward, the varied kinds and double-rooted 

 implantation of the teeth — all unequivocally displayed in this unique fossil — establish 

 beyond question the conclusions deduced from the foregoing specimens of the existence of 

 a small insectivorous Mammal during the Lower Oolitic epoch. 



Dr. BucKLAND kindly transmitted to me this specimen, soon after it came into his 

 possession, and acceded to my request to make some further explorations with a view to 



