DISTRIBUTION OF MAMMALS IN TIME. 559 



furnished with large and deep convolutions than is the case 

 with any other Mammal. The mammae are pectoral, and the 

 placenta is discoidal and deciduate. 



Man is the only terrestrial Mammal in which the body is 

 not provided with a covering of hair. 



The zoological or anatomical distinctions between Man and 

 the other Mammals are thus seen to be of no very striking 

 nature, and certainly of themselves would not entitle us to 

 consider Man as forming more than a distinct order. When, 

 however, we take into account the vast and illimitable psychical 

 differences, both intellectual and moral differences which 

 must entail corresponding structural distinctions between 

 Man and the highest Quadrumana, it becomes a question 

 whether the group Bimana should not have the value of a 

 distinct sub-kingdom ; whilst there can be little hesitation in 

 giving Man at any rate a class to himself. 



CHAPTER LXXXV. 



DISTRIBUTION OF MAMMALIA IN TIME. 



As a matter of course, the remains of Mammals are scanty, 

 and occupy but a small space in the geological record, since 

 the greater number of the Mammalia are terrestrial, and the 

 greater number of the stratified fossiliferous deposits are marine. 

 The Mammals, too, are the most highly organised of the entire 

 sub-kingdom of the Vertebrata; and therefore, in obedience to 

 the well-known law of succession, they ought to make their 

 appearance upon the globe at a later period than any of the 

 lower classes of the Vertebrata. Such, in point of fact, is to a 

 great extent the case ; and if the geological record were perfect, 

 the law would doubtless be carried out to its full extent. 



It is in the upper portion of the Triassic Rocks that is to 

 say, not long after the commencement of the Mesozoic or 

 Secondary epoch that Mammals for the first time make their 

 appearance ; four species being now known in a zone of rocks 

 which are placed at the summit of the Trias, just where this 

 formation begins to pass into the Lias. The earliest of these 

 the oldest known of all the Mammals appears at the upper 

 part of the Upper Trias (Keuper) and also at its very summit 

 (Penarth beds), and has been described under the name of 

 Microlestes antiquus. The nearest ally of Microlestes amongst 



