THE LARGER FOSSIL FORAMINIFERA OF THE PANAMA 



CANAL ZONE. 



By Joseph Augustine Cushman. 



Of the United States Geological Survey. 



INTRODUCTION. 



The foraminifera, especially the larger forms of the orbitoids, have 

 been little used in America as critical index fossils, except in the 

 Vicksburg group; but in Europe, Asia, and the East Indies they 

 have long been used to distinguish horizons. In many geologic 

 papers one finds Orbitoides mentioned, probably Orbitoides mantelli 

 Morton, and occasionally O. dispansus, 0. forbesi, etc. From a crit- 

 ical study of the group it soon becomes evident that such identifica- 

 tions as have been made of American orbitoids, except those of 

 Lemoine and Douville, have been largely superficial, and are there- 

 fore of little value. Since the earlier work of Giimbel the orbitoid 

 foraminifera have with further study been divided largely into the 

 four genera Orbitoides, Orthophragmina, Lepidocyclina, and Mio- 

 gypsina, in general respectively characterizing Cretaceous, Eocene, 

 Oligocene, and Miocene formations, but with important exceptions. 

 The American forms, with the exception of the work of Lemoine and 

 Douville, have not been properly referred to their respective genera, 

 although our American Orbitoides mantelli, described by Morton as 

 Nummulites mantelli in 1833, is the type-species of Lepidocyclina: 

 In their work on Lepidocyclina Lemoine and Douville x describe two 

 new American species, L. canellei and L. chaperi, from the Panama 

 Canal Zone, figuring also for the first time the critical chambers of 

 L. mantelli (Morton). These are all the American species that are 

 given, although they call attention to the apparently superficial char- 

 acter of the references to Orbitoides in American geologic papers. 

 Schlumberger, in his classic works on the genera Orbitoides and 

 Orthophragmina, did not have American material. The American 



1 Sur le Genre Lepidocyclina Giimbel, M6m. Soc. Geol. France, Paleontologie, Mem. 32, 

 1904. 



89 



