24 PROPESSOK OWEIs' ON THE CHARACTERS, ETC. 



the order, consisting of the genera Myrmecojphaga, or true Ant- 

 eaters, Dasypm or Armadillos, and Bradypus or Sloths, are con- 

 fined to South America. 



Having defined the orders or subdivisions of the two foregoing 

 subclasses, I may remark that the Lyencephala cannot be re- 

 garded as equivalent merely to one of the orders, say Bodentia, 

 of the LisseHcephala, without undervaluing the anatomical cha- 

 racters which are so remarkable and distinct in the marsupial and 

 monotrematous animals. The anatomical peculiarities of the eden- 

 tulous Lyencephal'a* appear to me to be, at least, of ordinal im- 

 portance. In these deductions I hold the mean between those 

 who, with Geoffroy St. Hilaire, would make of the Monotremata a 

 distinct class of animals, or with De Blainville, a distinct subclass 

 {OrnithodelpJies) of Mammals f, and those who, with Cuvier, would 

 make the Monotremes a mere family of the Edentata^ or, with 

 Mr. "Waterhouse, a family of the MarsvpiataX- In like manner, 

 whilst I regard the Lyencephala {Marsupiata of Waterhouse) as 

 forming a group of higher rank than an order, I do not consider 

 it as forming an equivalent primary group to that formed by all 

 the placental Mammalia. 



It appears to me that the true value of the Lyencephala or Im- 

 placentaliag is that of one of four primary divisions or subclasses of 

 the Mammalia ; that its true equivalency is with the Lissencephala, 

 and that all its analogical relations are to be found more truly in 

 that smooth-'brained subclass than in the Placentalia at large. 



The following Table exemplifies the correspondence of the groups 

 in the Lyencephalous and Lissencephalous series : — 



Lyencephala. Lissencephala. 



Bhizophaga^ Burrowing Bodentia. 



Poephaga^ Dipodidce and Leporidcd. 



Petaurus Pteromys. 



PhalangistidcB Sciuridce and prehensile-tailed 



arboreal Rodents. 



Phascolarctos Bradypus. 



Perameles and. Myrmecohius Erinaceidce. 

 Chceropus Macroscelis. 



* See my article Monotremata, in the Cy clopsedia of Anatomy, part xxvi. 1841 . 

 t Osteographie, fascicule premier, 4to, 1839, p. 47. 

 X Nat. Hist, of Mammaha, part i. 1845, p. 18. 



§ See the • Classification of the MarsupiaUa,' in the Zoological Transactions, 

 vol. ii. p. 232. 



