1072 Evolution of Mammalian Molars. 
triangle elevated and its cusps connected by cutting crests; a 
low posterior heel. b. This type embraces a quinquetubercular 
form in which the heel consists of two cusps, an internal and 
external.’ c. In the Bunodont series it develops into the quadri- 
_ tubercular form , by the loss of one of the primitive cusps. 
UPPER MOLARS. 
B. Tritubercular. a. The primitive triangle in the secodont series 
purely tricupsid. 6. This embraces a quinquetubercular form 
_,in which “ intermediate” tubercles are developed, both in the 
Secodont and Bunodont series. c. In the Bunodont series 
a postero- Npa] cusp is added, forming the sextubercular 
molar. 
NOMENCLATURE OF THE Cusps—As above stated, there is no doubt 
_ about the homologies of the three “ ‘primary ” cusps (proto- 
: cone, paracone, metacone) in the upper and lower molars 
. They may be given the- same terms, with the arbitrary suffix 
id, to distinguish the lower cusps. The first “ secondary ” 
cusps (hypucoue-hypoconid), added to the upper and lower 
, molars of the primitive triangle, modify the crown from a tri- 
angular to a quadrangular. shape, and hence may be, considered 
homologous. The three additional secondary cusps (protocon- 
ule, metaconule, entoconid) evidently have no homology with 
each other. 
TERMS NOW IN USE. PROPOSED TERMS.* ABBREV* 
Upper Molars. 
Antero-internal eS ee Protocone. pr- 
Postero- or Bth CUBD. oc seco ces eae. Hypocone. . 
Antero-external ‘ Swen eueeesectbaceuee ses ests Paracone. 
A he tee eae ee Cre rae ey eee eee Metacone. m. 
pararion Intermediate cusp E R Protoconule. pl. 
EROF SO e Eei Metaconule. ml. 
OT Molars. : 
Antero-external ia 0d “etal ares ta dese Protoconid. ` pr 
OO eg etd POU e eaa Hypoconid. . 
Raterointerial cusp, or 5th cusp........-.---- Parrconid. P. 
Fa totagdiste or antero-internal cusp (in quad- 
ritube molars) Metaconid m. 
Postero-internal RO ee ee arene weer 2 Eutoconid. e. 
Evolution of the Cusps. The cusp evolution in the Mesozoic 
period has been fully discussed by the writer (op. cit., pp- 240 4) 
1 American Naturalist, April, 1883, p. 407. 
2 I am much indebted to my colleagues Professors 
Winans for tie assistance in the selection of these terms. 
