Coryphodon aier: Cope. It is quite unnecessary to complete 
1102 Recent Literature. [Dec, 
to find in this memoir a history of the evolution of Mammalian 
dentition will be disappointed, for it embraces only a history of — 
the evolution of the milk-dentition and the nature of dental — 
succession. To this end the author has written a very useful 
paper, and illustrates it with numerous instructive diagrams and 
He first describes the dentition of the Dasyuride, and 
single skull of Phascogale dorsalis a supernumerary tooth between 
the first and second premolars. In our opinion, this super- 
numerary tooth, if anything more than an abnormality, can only 
represent a former tooth of a series of five. Similar teeth have 
been‘ observed in the inferior series in Miacis edax Leidy, and 
i 
a 
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the number of four premolars, since four are accounted for, after 
the replacement of the third, which is wanting in Dasyurus. 
The fourth is of molariform structure, and has been the 
regarded as a true molar by Flower and Thomas. The fact 
it is in the genus Triisodon and probably others (as Mioclænus, 
where there aré four inferior premolars), shed and Sucre w 
ogy, as I have pointed out” Mr. Thomas finds. my description 
of this genus “incomplete and confusing,” and the reaso 
he does so is apparent from the above descriptic 
r. Thomas believes that the milk-dentition 1s n heh 
of a primitive succession derived from Reptilian ancestor ee 
holds, with Professor Flower, that it is a superaddition gra mi us 
introduced in the evolution of the Mammalia. e lack of milk 
teeth other than the third premolar (or its homologue), a 
of Flower. On this view it appears that the placen 
to the implacental milk-dentition one tooth posterior 
anteriorly. It then looks as if the deciduous dentition 
of primitive teeth retarded in their protrusion by more Fo” 
ones. This is essentially Mr. Thomas's explanation, metho 
approximates that of Baume, who, however, differs in Me © 
= Final Report U. 8. Geol. Survey Terrs.» il. Bk. i. By 22% 12> 
r 
