INTRODUCTION 



Professor Cope 1 appropriately named it the tritubercular ////"'.- By com- 

 parison with the teeth of more recent animals, the further conclusion 

 was reached that the tritubercular f ///>< n-as ancestral to many if not to all 

 of the higher types of molar teeth. This is one of the most important 

 generalizations ever made in mammalian comparative anatomy ; it 

 outranks in importance the proof of the primitive pentadactyl nature 

 of the feet of hoofed animals. In the writer's opinion, the evidence in 

 favour of it is so overwhelming that primitive trituberculy is no longer 

 an hypothesis or a theory, but an established fact. In the accompany- 

 ing table it will be seen that those orders in which generalized ancestral 

 forms are positively known to possess tritubercular molar teeth (I) 

 and those orders in which primitive tritubercular teeth or some of 

 the immediately derivable types are occasionally observed, although 

 the line of descent has not actually been traced (II), far outnumber 

 those (III) in which we must reason by analogy, because we have as 

 yet no positive light on the descent of the teeth. 



I. 



Mammalian orders in which 

 ancestral forms are posi- 

 tively known, which exhibit 

 tritubei'cular or plainly de- 

 rived types of molars. 



Edentata TYeniodonta 



(Ganodonta) (p. 151). 

 Insectivora primitive 



(Mesozoic) (pp. 26-30). 

 Insectivora (p. 117). 

 Marsupialia Polyproto- 



dontia (cf. Oligocene 



Perat/ierium, p. 1U9). 

 Carnivora Creodonta (p. 



131). 

 Oarnivora Fissipedia (p. 



135). 



Tillodontia (p. 151). 

 Primates (p. 157). 

 Amblypoda (e.g. Panto- 



lambda p. 165). 

 Condylarthra (e.g. Proto- 



gonodon, p. 169). 

 Artiodactyla (e.g. Trigono- 



lestes, Homacodon, p. 



171). 

 Perissodactyla (e.g. Hyra- 



coth eriv.m, Systemodon^ 



p. 174). 



II. 



Orders in which tritubercular 

 or plainly derived types 

 of molars are occasionally 

 observed although the line 

 of descent has not actually 

 been traced. 



Marsupialia Diproto- 



dontia (p. 109). 

 Rodentia Duplicidentata 



(p. 148). 

 Rodentia Simpliciden- 



tata (p. 146). 



Ancylopoda (cf. Schizo- 



tln'rium, Chalicotherium, 



(p. 184). 



Zeuglodontia (p. 191). 

 Hyraeoidea (p. 185). 

 Proboscidea (e.g. Mceri- 



therui.m, p. 186). 

 Sirenia (cf. Halitherium 



veronense, p. 189). 

 Toxodontia and other 



South American Ungu- 



lata (p. 189). 



Ill 



Orders in which we have as 

 yet no positive light on the 

 descent of the molars. 



All other Edentates (p. 



152). 



Monotremata (p. 107). 

 Multituberculata (p. 101). 

 Cetacea 3 (p. 190). 

 Carnivora Pinnipedia (p. 



143). 



1 American Natural i*t, April, 1883, pp. 407-408. 



2 N. B. The lower molars generally show also a talonid or heel. 



3 Zeuyhdon not included. 



