ORDINAL TYPES OF MOLARS: MONOTREMATA 105 



4. Some additional evidence on this point is derived from the study of 

 the dentition of the molar teeth of the Monotremes (p. 107). 



5. Still another possibility is that the molar form of Microlestes 

 antiquus may be derived from that seen in Phascolotherium by the 

 upgrowth of heavy cusps from the internal ciuguluni (compare Fig. 48, 

 No. 1, and Fig. 6). 



6. Again, this molar might represent a pattern allied to that of the 

 Amphitherium molar (Figs. 15, 17), that is the highest anterior (?) cusp 

 above the anterior (?) root (Fig. 48, Nos. la, Ib) may be a protoconid, 

 the first cusp on the opposite side of the tooth a metaconid, and all that 

 portion of the tooth above the second root may be the talonid. Or again, 

 the Microlestes molar might have been derived from that of the Amblo- 

 theriida- by the upgrowth of the cingulum cusps on the inner sides of 

 the crown and the loss of the transverse connecting ridge.* 



SPECIAL REFERENCES. 



Ameghino, F., "Los Diprodontes del Orden de los Plagiaulacicleos y el Origen de 1< 

 Roedores y de los Poliniastodoutes," Anales del Mus. Nac. de Buenos Aires, Tom. IX., 

 1903, pp. 81 a 192. 



Osborn, H. F., " The Structure and Classification of the Mesozoic Mammalia,'' 

 Jour. A cad. Nat. Sci. Phila., Vol. IX., No. 2, July, 1888. 



Owen, Richard, " Monograph of the Fossil Mammalia of the Mesozoic Formations," 

 Palceontogr. Soc. Lond., 1871. 



Owen, Richard, "On the Skull and Dentition of a Triassic Mammal (Tritylodon 

 longcevus)" from South Africa ; Qtir. .l<mr. Oeol. Soc., 1884. 



Lemoiue, Victor, "Etude sur le Neoplagiaulax de la Faune Eocene inferieur d-s 

 Environs de Reims," Extr. Bull. Soc. Geol. de France, Feb. 1883. 



Cope, E. D., "The Tertiary Marsupialia," Amer. Naturalist, 1884, p. 687. 



Marsh, O. C., "The American Jurassic Mammals," Amer. Jour. Sci. and Arts., 

 April, 1887. 



Marsh, O. C., " Review of Osborn's Memoir on the Structure and Classification of 

 the Mesozoic Mammalia," Proc. Acud. Nat. Sci. Phila., June, 1887. 



Falconer, H., "On the disputed Affinity of the Mammalian Genus Plagiaulax from 

 the Purbeck Beds," Collected Memoirs, Vol. II., pp. 430-451. 



MONOTREMATA. 



The true molars of OrnithorhyncJms when first described (Poulton, 1 

 1888) were adduced by Cope as inultituberculate and as tending to 

 demonstrate the affinity of the Multituberculata to the Monotremata. 

 When critically examined, however, the molars of Ornitkorhynchus are 

 found to be very degenerate both in structure and in pattern, and it 



* [Against all these speculations one might advance another speculation, that Microlexti s, 

 Tritylodon and the Multituberculates, appearing iu the Triassic, were not closely related 

 to trituberculate mammals (which are first known in the Upper Jurassic or Basal Cretaceous) 

 but were independent offshoots from the Tlieriodontia. -En.] 



1 Poulton, E. B., "The True Teeth and the Horny Plates of Ornif/ior/n/ii,-!,,!*." V'""'- 

 Jour. Microsc. Sci, Vol. XXIX., Aug. 1888. 



