64 SECONDARY SERIES. 



of general occupation by warm-blooded terrestrial Mam- 

 malia. 



The only terrestrial Mammalia yet discovered in any se- 

 condary stratum, are the small marsupial quadrupeds allied 

 to the Opossum, which occur in the oolite formation, at 

 Stonesfield, near Oxford. The jaws of two species of this 

 genus are represented in Plate 2. a. b; the double roots of 

 the molar teeth at once refer these jaws to the class of Mam- 

 malia, and the form of their crowns places them in the or- 

 <icr of Marsupial animals. Two other small species have 

 been discovered by Cuvier, in the tertiary formations of the 

 basin of Paris, in the gypsum of Mont Martre. 



The Marsupial Order comprehends a large number of 

 existing genera, both herbivorous and carnivorous, which 

 are now peculiar to North and South America, and to New 

 Holland, with the adjacent islands. The kangaroo and 

 opossum are its most familiar examples. The name of 

 Marsupialia is derived from the presence of a large external 

 marsupium, or pouch, fixed on the abdomen, in which the 

 foetus is placed after a very short period of uterine gestation, 

 and remains suspended to the nipple by its mouth, until 

 sufficiently matured to come forth to the external air. The 

 discovery of animals of this kind, both in the secondary 

 and tertiary formations, shows that the Marsupial Order, so 

 far from being of more recent introduction than other orders 

 of mammalia, is in reality the first and most ancient condi- 

 tion under which animals of this class appeared upon our 

 planet: as far as we know, it was their only form during the 

 secondary period ; it was co-existent with many other or- 

 ders in the early parts of the tertiary period; and its geogra- 

 phical distribution in the present creation, is limited to the 

 regions we have above enumerated.* 



* In a highly important physiological paper, in the Phil. Trans. Lon- 

 don, 1834, part ii. p. 349, Mr. Owen has pointed out " the most irrefra- 

 jrible evidence of creative foresight, afforded by the existing Marsupialia, 

 in the peculiar modifications both of the maternal and foetal system, de- 



