102 THE FOEAMINIFERA 



genus, and in adult forms is composed of many 

 superposed layers of cliamberlets, the number of the 

 layers increasing as the shell advances in growth. 

 Sometimes this species loses its regularly discoidal 

 contour and, growing attached to algae and other 

 marine objects, becomes more or less sinuous and 

 irregular. 



Owing to the thinness of the wall of the primor- 

 dial segment, and to the fact that it usually 

 protrudes beyond the general surface of the test, 

 the specimens found in shore sands, where they are 

 exposed to weather action, are often found perforated 

 in the middle. The natives of coral islands often 

 take advantage of this, and select the larger speci- 

 mens (often half an inch or more across) to sew into 

 the native dresses for decorative purposes. 



There is a large variety of 0. comjdafiata known 

 as variety plicata (Dana), or variety Jaciniata 

 (Brady), in which the edge of the disc is double and 

 is also frilled. This condition of the shell was 

 shown by H. B. Brady and other observers to 

 contain the megalospheric young of the species, 

 enclosed in large chamberlets arranged around the 

 periphery. This particular variety is only found in 

 tropical areas, and usually in the neighbourhood of 

 coral reefs, in quite shallow water. 



0. comjdanata, apparently first appeared in the 

 Maestricht beds (Upper Cretaceous), and continued 

 on to the present day. (Plate 4, figs. F, /.) 



