26 
EDWARD B. POBLTON. 
be applied as tests to teeth in such early stages of development. 
The existence of different kinds of teeth has been proved in 
the upper jaw, and the presence of many distinct cusps has 
been abundantly shown. In my short preliminary account 
alluded to by Professor Seeley (1. c.. p. 354, footnote) there is 
the statement: “ The two posterior (upper) teeth have many 
cusps.” In the present paper I think it has been proved that 
these teeth are not behind those of many mammals which, as 
Professor Seeley admits, possess “ a specialisation which is un- 
paralleled among reptiles.” Furthermore, Professor Seeley’s 
suggestion that “ there is a certain relation .... between 
the complexity of the crown and the complexity of the fangs ” 
is extremely probable, and leads us to conclude that the de- 
veloped teeth of Ornithorhyuchus must have possessed many 
fangs. If we finally add the important test of the presence 
of a highly-developed middle layer in the enamel organ, I 
think we cannot escape the conclusion that, whatever tran- 
sitional states may be met with iu certain characters of cer- 
tain teeth in other mammals, these teeth, in the most 
primitive mammal, show no indications of any such transi- 
tion, hut are essentially and typically mammalian. Of course 
I entirely agree with Professor Seeley as to the ultimate 
origin of mammalian teeth from the simpler reptilian type, and 
I should also agree in considering the differences as compara- 
tively unimportant ; and this latter consideration renders it all 
the more easy to understand how it is that the gap from rep- 
tilian to mammalian tooth-structure was crossed before the 
appearance of Monotreme life at its present level. 
Professor E. D. Cope, in ‘The American Naturalist’ for 
March, 1888 (p. 259), quotes the description of the form of 
the teeth from the abstract of my preliminary paper, printed in 
‘ Nature,’ February 16th, 1888, p. 383. He considers the 
subject of great importance in relation to the secondary mam- 
mals with multituberculate teeth. He states : “ The descrip- 
tion reads like that of the dentition of the Plagiaulacid genus 
Ptilodus. It renders it extremely probable that the 
