2 CONTRIBUTIONS TO PALZONTOLOGY 
Since the general problem of the Siwalik anthropoids is being dealt with 
in a monograph by G. E. Lewis, the present paper deals only with the 
material collected by the Yale-Cambridge Expedition of 1935. A brief 
synopsis of the nomenclature and synonymy of the Siwalik anthropoids, 
published by Lewis in August 1937, explains the great complexity of the 
nomenclatural problem and the reasons for reducing several widely used 
names (e.g., Dryomthecus cautleyz) to the rank of synonyms. 
The stratigraphic sequence and faunas of the Siwalik deposits having been 
described recently by Colbert (1935), by de Terra and Teilhard de Chardin 
(1936), and by Lewis (1937), we need say here only that in a general way 
the Siwalik fossil apes range from the uppermost middle Miocene to the 
middle Pliocene. Between the successive zones there is not always a sharp 
faunal break, at least in the anthropoid series. This accords with much 
evidence tending to show that in spite of their great thickness the older 
Siwalik deposits were built up during a relatively short period of rapid 
sedimentation. 
LIST OF SPECIMENS WITH PROVISIONAL DETERMINATIONS 
By agreement between the museums concerned, the primate material 
described below has been divided between the Peabody Museum of Yale 
University and the Indian Museum in Calcutta, as shown in the table on 
pages 3 and 4. The new specimens were collected mostly by Mr. Aiyengar. 
We have, of course, also restudied the specimens described by Lewis in 
1934 and by Gregory and Hellman in 1926. 
COMPARATIVE MEASUREMENTS OF SIWALIK 
ANTHROPOID THETH 
Since the degree of wear greatly affects the dimensions and proportions of 
the teeth, especially in the lower molars, we have prepared the following 
classification with reference to stage of wear: 
I. Unoccluded. No pressure or occlusal wear facets; enamel sculpture 
unaltered. Unerupted or just erupted. | 
II. Karly post-eruptive. Cusps show occlusal wear facets; proximating 
surfaces of adjacent teeth show pressure facets; enamel sculpture 
showing some wear but still preserved. 
III. Moderate. All enamel sculpture worn away except primary sulci 
indicating groove pattern (“Dryopithecus,” “cruciform,” etc.) ; no 
dentine exposed; pressure facets shown. 
IV. Advanced. Enamel worn away in places, forming pits in end, local- 
ized by the primary cusp points of underlying dentine; primary 
sulci still preserved; cusps still retain their identity at their bases; 
pressure facets shown. 
V. Extreme. Cusps and groove pattern obliterated; pressure facets 
pronounced; entire crown ultimately worn away on occlusal surface. 
