2 CALIFORNIA ACADEMY OF SCIENCES rPnoc. 4th Sek. 



Does the Lyell percentage system apply to tropical inverte- 

 brate faunas? In answering this question one must bear in 

 mind that this scale is really an expression of the time rate of 

 evolution of Tertiary molluscan faunas based upon the study 

 of the Tertiary of Europe. Briefly, this scale, as now generally 

 applied, is : Eocene, 0% ; Oligocene, 3% ; Miocene, 25% ; Plio- 

 cene, 60% ; and Pleistocene, 90%. Practically all the Eocene 

 molluscan genera exist today in the Recent faunas of the tropi- 

 cal and temperate zones. Great was our surprise to find that our 

 collections from the upper Vigo shales and the Canguinsa for- 

 mation, regarded by Pratt 1 and Smith as being of Lower Mio- 

 cene and Oligocene age, yielded a molluscan fauna containing 

 75% Recent species. The results of these preliminary studies 

 indicate, that a negative answer must be given to the rhetorical 

 question asked 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 be 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 specifically far more numerous than a 

 recent fauna from a temperate region. Hidalgo 2 reports 4300 

 to 4500 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. 



Professor K. Martin 3 in "Tertiarschichten auf Java" recog- 

 nized in a general way that the percentage system of Deshayes 

 (and Lyell) did not strictly apply in Java and that climatic 

 variation was a prime cause of this difference. 



Brief Statement of Geological History 



The fauna upon which this paper is based was collected from 

 the southern half of the Bondoc Peninsula from strata referred 



1 Pratt, W. E., and Smith, W. D., "The Geology and Petroleum Resources of the 

 Southern Part of Bondoc Peninsula," Tayabas Province, P. I., Phil. Jour. Sci., 

 Vol. VIII, 1913, Sec. A, No. 5, p. 312. 



2 Hidalgo, J. G, Catalogo de los Moluscos Testaceous de las Islas Filipinas, Jolo y 

 Marianas, p. 389, Madrid, 1904-1905. 



3 Martin, K., Die Tertiarschichten auf Java, p. 22-24, Die Lagerunas vethaeltnisse, 

 Leiden. 1880. 



