The Philippine Journal of Science 1921 
evolution of Tertiary molluscan faunas based upon the study of 
the Tertiary of Europe. Briefly, this scale as now generally 
applied is: 
Period. Per cent. 
Eocene 0 
Oligocene 3 
Miocene 25 
Pliocene 60 
Pleistocene 90 
Practically all the Eocene molluscan genera exist to- day in 
the Recent faunas of the tropical and temperate zones. Great 
was our surprise to find that our collections from the upper 
Vigo shales and the Canguinsa formation, regarded by Pratt 
and Smith: as being of lower Miocene and Oligocene age, 
yielded a molluscan fauna containing 75 per cent Recent species. 
The results of these preliminary studies indicate that a negative 
answer must be given to the rhetorical question stated above. 
An essential modification of the Lyell percentage scale seems 
necessary to the writer for the proper interpretation of the 
Tertiary faunas of the Tropics. If this hypothesis is true then 
evidently marine molluscan faunal changes take place with far 
less rapidity in the Tropics than in the temperate zones. Now 
this conclusion is apparently in direct contradiction to the fact 
that the Recent molluscan fauna of the Philippines is speci- 
fically far more numerous than a Recent fauna from a temperate 
region. Hidalgo? reports from 4,300 to 4,500 land, terrestrial, 
fluvial, and marine testaceous mollusca, and of these fully two- 
thirds are marine. This anomaly will be considered after the 
presentation of the data. 
Prof. K. Martin * recognized in a general way that the per- 
centage system of Deshayes (and Lyell) did not strictly apply 
in Java, and that climatic variation was a prime cause of the 
differences. 
BRIEF STATEMENT OF GEOLOGIC HISTORY 
The fauna upon which this paper is based was collected from 
the southern half of the Bondoc Peninsula from strata referred 
by Pratt and Smith to the Canguinsa formation and Vigo 
*Pratt, W. E., and Smith, W. D., The geology and petroleum resources 
of the southern part of Bondoc Peninsula, Philip. Journ. Sci. § A 8 (1913) 
312. 
* Hidalgo, J. G., Catalogo de los Moluscos Testdceos de las Islas ee 
Jol6 y Marianas. Madrid (1904-1905) 389. 
* Martin, K., Die Tertiarschichten auf Java, Die Lagerunas verhaelt- 
nisse. Leiden '(1880) 22-24. 
