214 



GREGORY: NOTHARCTVS, AN AMERICAN EOCENE PRIMATE 



tympanic sinus covering tympanic ring but separated from it by membrane. Brain macrosmatic, but 

 with wider frontal lobes. 



Stage 3. — Pleistocene and Recent Lemuridse. Diet various, more insectivorous in some, more 

 frugivorous in others. Tongue enlarged. 1^2° P| M|. Lower front teeth highly specialized. P2 

 enlarged and subcaniniform. Dentition more or less degenerate and speciaUzed: paraconids of lower 

 molars, protoconules, metaconules and cingula of upper molars and metacone of p"* usually lost or greatly 

 reduced. Premolars simplified; metacristid and talonid often enlarged; hypoconulid of ms more or 

 less reduced. Jaw typically slender. Muscle crests typically degenerate, zygomata usually weak. 

 Orbits typically enlarged. Lacrymal expanded on face. Brain-case usually much expanded, exposing 

 supraoccipital plus interparietals on top of skull. Membrane between hypotympanic sinus and tym- 

 panic ring reduced or absent, the latter lying freely within the bulla. Brain becoming microsmatic, with 

 large, usually well-furrowed cerebra partly overlapping large cerebellum. 



COMPARISON OF XOrilARCn'S WITH THE IXDRISID.E 

 Plates LVI~LVIII 



The general contrast in dentition and skull between Notharctus, representing a primitive Eocene 

 lemuriform stock, and Propithecus, representing the highly modernized lemuriform family Indrisidse, 

 is as follows (P., progressive; Prim.^ primitive; R., retrogressive): 



Dental Formula 

 Probable Diet 



Probable Deciduous Formula 

 Lower Incisors 



Lower Canines 

 Pi, P3 



P2 



P4 



Lower Molars 



" " Entoconids 

 M3 Hypoconulid 

 Upper Molars 



Proportions : anteroposterior elonga- 

 tion 



Lingual Cusps 

 V\ p3 

 V\ p4 



Muzzle 

 Orbits 



Frontal Sinus 

 Lacrymal Foramen 

 Malar 



Glenoid Fossa 



Notharctus 



1.2 1 1.2.3.4 1.2.3 

 Insectivorous-frugivorous 

 DI^^I DC; DMgf 



Two pairs gently procumbent, short, 



subspatulate 

 Erect, subcaniniform 

 Present 



Small, simple 



Primitive 



Tuberculosectorial 



Low 



Well de\-eloped 



Moderate 

 Subconic 

 Present 

 Primitive 



Moderately long 



Moderate 



Small 



Marginal 



Moderate 



Shallow 



Propithecus 

 (R) I L2 F ' ' M^^' 



1 2 '-I 1*2.4 -^'-^1.2.3 



Leaves, fruits, flowers 



(Prim) DI^ DC; DPf|i 



(P.R) One pair, sharply procumbent 



styliform 

 Procumbent, styliform 

 (R) Pi vestigial, lost with deciduous 



teeth, p3 lost 

 (P) Enlarged, compressed, opposing p^ 



and c 

 (P) Compressed 

 (P) With W-shaped crowns 

 (P) High 

 (R) Aborted 



(P) Pronounced 



(P) Sharply-V-shaped 



(P) Absent 



(P) Compressed with reduced internal 



cusps (R) 

 (R) Short and wide 

 (P) Larger, extended laterally 

 (P) Enlarged 

 (P) Preorbital 

 (P) Robust 

 (P) Deep 



* Vestigial, appearing with the milk dentition, but very early shed. 



