208 MEMOIRS OF THE CARNEGIE MUSEUM 
YELATIONSHIP. 
The general appearance of the skull is strikingly like that of the Monotremes. 
In fact, with the exception of the presence of tympanic bulle and rooted teeth, 
it differs in no essential particular from Ornithorhynchus or Hchidna. The presence 
or absence of tympanic bullee has little significance in this connection, as it has been 
independently developed in so many widely different mammals. The Monotremes 
have a tympanic ring. In some cases this may have developed into a bulla. 
The teeth differ from those found in Oriithorhynchus in being peg-shaped, and in 
being set in quite deep and well-defined alveoli. The number is also greater than 
in the latter genus, there being, apparently, six in each side of the jaw instead of 
two or three. In the new genus, too, there was one tooth which was caniniform. 
In Ornithorhynchus, the teeth, which are -low-crowned, appear to have small roots. 
But when we consider the vast dissimilarity in the different teeth of some indi- 
viduals —for example, in certain Multituberculates, Insectivores, Marsupials, ete.— 
to say nothing of the astonishing differences and variety in the structure of the teeth 
in the subclass Eutheria, we could hardly exclude this animal from the Monotre- 
mata on these grounds. In fact, they appear quite insignificant. That the Mono- 
tremes have had a long history, and that they developed into aconsiderable diversity 
of forms is made evident by the marked minor differences of the two or three exist- 
ing genera. 
But since the idea of development has taken possession of biologists there has 
been a great temptation to see relationship where none exists. There is a vast 
interval, both in time and space, between early White River times in the Rocky 
Mountains and the Australian region of to-day, and we have but a single skull by 
which to judge. Yet if we were looking for a Monotreme in these older beds we 
could hardly expect it to be so much like that of the living species as is the fossil. 
The general appearance of the skull is most like that of Echidna; though in a 
few details it more resembles Ornithorhynchus. If we could take a skull of Echidna, 
shorten its muzzle, give it tympanic bulle and simple cylindrical teeth, make the 
orbito-temporal fossa like that of the duckbill, and premaxillaries similar to those 
of the latter, but much shorter, we would have a skull similar in all its principal 
characters to the fossil. 
If this is the skull of a Monotreme it certainly is of great interest. If not, it is 
perhaps even more so; as, so far as I can learn, there is nothing like it among the 
Eutheria. 
