22 MAMMALIA class v 



The marsupial bones, paired rod-like ossifications attached to the foremost 

 extremity of the os pubis, are a peculiarly distinctive feature of the group. 

 They are found in both sexes, but in the genus Thylacinus are represented only 

 by a small, unossified fibro-cartilage. Frequently the length of the hind-limbs 

 exceeds that of the anterior pair. The pes (Fig. 26) has either five or four toes, 

 of which the fourth is the largest. The second and third among herbivorous 

 marsupials become very slender, and are enclosed nearly to their extremities in 

 a common integument. There exist, nevertheless, many transitions between 

 this highly specialised form and the original five-toed foot. The hallux is often 

 at right angles to the rest of the toes, in some cases even being eliminated 

 entirely. Dollo traces the development of all marsupials from pentadactyl 

 arboreal ancestors. 



With the exception of the Didelphiidae, extensively found in America, and the 

 South American Caenolestidae, the habitat of marsupials is at present restricted 

 to Australia and the neighbouring islands. The Pleistocene forms of this order 

 were similarly distributed. In the Jurassic, Cretaceous and Tertiary, however, 

 fossil marsupials are found not only in America, but also, to a great extent, in 

 Europe. Marsupials may be divided for purposes of practical convenience into 

 three suborders, as follows: Allotheria, Diproiodontia and Polyprotodontia. The 

 family Caenolestidae may be considered transitional between the last two. 



Suborder A. ALLOTHERIA Marsh. 



(Multituberculata Cope.^) 



Small extinct herbivorous w omnivorous mammals with polyhunous M, the tubercles 

 of which are arranged in tiw or three longitudinal series. P similar to M but simpler 

 or laterally compressed. Each jaw with one strongly developed rodent-like I. No C. 

 Lower jaw nsually with inflected angle. Cm'acoid perhaps separately developed. 



Eemains of Allotheria have been found in the Trias of Europe and South 

 Africa, in the Jura of Europe and North America, in the Cretaceous of North 

 America and in the basal Tertiary of Europe and North America. Probably 

 here should be placed also several forms from the Eocene of South America. 



Most of the genera are represented by isolated teeth, mandibles, and more 

 rarely portions of the upper jaw and cranium. The complete skull and various 

 bones are known onl}' in the genus Ptilodus. The systematic position of many 

 forms is therefore very uncertain. Nevertheless the greater number of forms 

 may be regarded as marsupial. It has been shown by Matthew that Cope 

 was in error in referring an astragalus to Polymastodon. 



Family 1. Tritylodontidae Cope. 



Snout truncated, premaxillary tvith one stout canine-like I, followed by a small 

 pointed I. P similar to M, but simpler ; M with three rows of tubercles. Trias ; 

 South Africa and Europe. 



^ Ameghiiw, F., Anales Mus. Nac. Buenos Aires, vol. ix., 1904. — Cojje, E. D., Amer. 

 Naturalist, 1881, vol. Ixxxvi. — Broom. R., Bull. Amer. Mus. Nat. Hist., vol. xxxiii., 1914. — 

 Gidley, J. W., Proc. U.S. Nat. Mus., vol. xxxvi., 1909, p. Qll. —Hennig, E., Neues Jahrb. f. 

 Min., Beil.-Bd. 46, \^22.—Lemoine, V., Bull. Soc. Geol. France, 1883, 3 stiT.— Marsh, 0. C, 

 Amer. Journ. Sci., 1878-81; 1889: 1892. —Os6om, H. F., Journ. Acad. Nat. Sci. Philad., 

 vol. ix., 1888. — Proc. Acad. Nat. Sci. Pliilad., 1891. Amer. Naturalist, July 1891.— Bull. Amer. 

 Mus. Nat. Hist., 1893. 



