Evolution of Mammalian Molars. 1071 
I. Haplodont Type (Cope)! A simple conical crown. The 
fang usually single and not distinguished from the crown. This 
type has not as yet been discovered among the primitive Mammalia. 
A Protodont Tub. Type.2 The crown with one main cone, and 
lateral accessory Cuspules ; the fang grooved. There is some ques- 
tion as to the advantage of distinguishing this as a type, for it stands 
intermediate between types I. and III. Example, Dromotherium 
of the American Triassic. 
II. Triconodont Type (Osborn, op. cit., p. 242). The crown 
elongate, trifid, with one central cone and two distinct lateral cones 
The fang double. Example, Triconodon. 
II. Tritubercular (Cope). The crown triangular, surmounted 
by three main cusps, the central cone placed internally in the upper 
mollars and externally in the lower molars. Example, the lower 
molars of Spulacotherium and Asthenodon. This type is rare in its 
primitive condition as above defined. 
e upper and lower molars are alike in types I. and II.; in 
type III. they have a similar pattern but with the arrange- 
ment of the homologous cusps reversed. These types are all 
primitive. In the following sub types, the primitive trian- 
gle forms the main portion of the crown, to which other 
“secondary” cusps are added, the homologies of which in the 
upper and lower molars are somewhat doubtful. Parallel 
and with an intimate relation to the addition of the secondary 
cusps, is the division of the tritubercular into a secodont and 
bunodont series, according to the assumtion of a purely cut- 
ting or crushing function. In departing from the primitive 
type, the upper and lower molars diverge in structure, and the 
homologies of the secondary cusps in each are somewhat — 
doubtful, 
LOWER MOLARS, 
A. Tubereular Sectorial, sub type (Cope). a. The primitive 
'“ The Homologies and Origin of the Types of Molar Teeth in the 
Mammalia Edueabilia.” Journ. Phila. Acad., 1874. The term Homo- 
dont was previously applied to this type by Riitimeyer, ‘‘Udonto- 
graphie der Hufthiere, ete.” Verh. d. Naturforsch, Gesellsch. in Basel, 
Band. III., 1863, p. 563. In the writer’s opinion this term has acquired 
-a special significance as applied to a whole series of teeth, viz., the re- 
verse of ‘‘ heterodont,’’ and may well be retained in this sense. 
? Osborn, op. cit., p. 222. 
