92 AN INTRODUCTION TO THE STUDY OF FOSSILS 



incloses the preceding by means of a lateral prolongation of the 

 chambers. The aperture is an inconspicuous slit at the inner 

 margin of the last chamber. In Nummulites the increase in 

 size is mainly on the periphery, in Fusulina it is mainly axial. 

 A large and a small form are usually found associated in the 

 same rock ; these most probably are the large sexually produced 

 test, and the small, asexually produced test of the same species. 



Nummulites occur from the Penn- 

 sylvanian to the present, but sparsely 

 outside the Tertiary. The one or two 

 forms now living, as off the southeast 

 coast of Asia, are tropical and sub- 

 ^, , , ^ , tropical. Nummulites attained their 



Fig. 33. — The skeleton of a ^ _ 



marine protozoon, Niimtnuii- maximum abundance during the Eo- 

 /.5, from the Eocene of Egypt. ^ making limestone masscs, — 



A very small specimen en- ' '^ ' 



larged. A, surface view of nummulitic limestone, up to several 

 the coin-like shell. 5 section thousand feet in thickness, in the 



parallel to the flat surface. _ \ 



East Indies, Japan, South Asia, South 

 Europe, North Africa and Central America. The largest species 

 in these rocks attains a diameter of 60 mm. ; the smallest, 2 mm. 

 Associated with these Nummulites are other marine forms, such 

 as mollusks and corals. The great pyramid of Cheops is built 

 of this limestone. 



1. Sketch (a) surface view, (b) longitudinal section, (c) trans- 

 verse section. A thin section made from nummulitic limestone 

 will usually give the above sections. 



2. How does this differ in its manner of coiling from Fusulina ? 



3. What is the significance of the name? 



4. When and where did it occur most abundantly ? 



5. Account for the large and small forms usually found asso- 

 ciated in the same rock. 



Orbitoides (Fig 34). Cretaceous to Miocene. 



General shape of test very similar to that of Nummulites, 

 but the chambers are smaller, much more numerous and com- 

 plicated. 



