112 



PROTOZOA. 



antly in the Mountain Limestone of Britain. It forms 

 in America entire beds of the Carboniferous Limestone 

 (fig. 20). In Trochammina (fig. 18, e) the test is usually 



spiral, consisting of one or 

 many chambers, free or at- 

 tached, and, though sandy, 

 with a smooth surface. It 

 ranges from the Carboniferous 

 to the present day. Valvu- 

 lina (fig. 21) also generally 

 has a spiral shell which may 

 be free or attached, and is 

 normally thick-walled, imper- 

 forate, and sandy. Sometimes, 



Fig. 20.-Section of Carboniferous Lime- however, the shell is pOTOUS 

 stone from Spergen Hill, Indiana, U.S., 



showing numerous large-sized Foraminifera and Smooth, and 111 Other 



(Endothyra) and a few oolitic grains mag- ,-, -, , . 



nified. (Original.) cases the sandy coating seems 



to be a mere incrustation on 



a calcareous and perforate shell, so that Valvulina may 

 be regarded as a transitional type between the great 

 series of the iinperf orate and perforate Foraminifera. The 



Fig. 21. A., Slice of limestone with Saccammina Carteri, enlarged 5 diameters ; B, Spheres 

 of the same, of the natural size, exhibiting variations ; c, Valvulina palceotrochus, in profile ; 

 and D, the same viewed from below, enlarged 45 diameters. All from the Carboniferous. 

 (After Brady.) 



genus makes its first appearance in the Carboniferous of 

 Britain, is abundant in the Tertiaries, and is represented in 



