24 PROTOZOA. FORAMINIFERA 



each coil usually covers the one preceding it. Cambrian to present 

 day. Ex. C. rotulata, Chalk. 



Globigerina. (fig. 3, 7, K.) Shell perforated by large canals ; 

 chambers globular, few, arranged in a plain or helicoid spiral, each 

 chamber opening by a large aperture into the central cavity of the 

 spire. No supplemental skeleton. Pelagic forms usually with 

 spines. Cambrian to present day. Ex. G. cretacea, Chalk. 



Orbulina. A single spherical chamber, with perforations of 

 two sizes. Sometimes with smaller chambers (similar to a Globi- 

 gerina) inside the large spherical one. Lias to present day. Ex. 0. 

 universa, Lias to present day. 



Rotalia. (fig. 3, L, If.) Test very finely perforated, multi- 

 locular. The chambers arranged in a helicoid spiral, so that on the 

 upper surface all the whorls are seen, on the lower only the last one. 

 The aperture is in the form of a curved slit on the lower surface of 

 the last chamber. The septa are usually formed of two layers. 

 A supplemental skeleton is often present. Lower Cretaceous to 

 present day. Ex. R. beccari, Miocene to present day. 



Calcarina. Test lenticular, spiral, with only the last whorl 

 visible on the base. Supplemental skeleton greatly developed, 

 traversed by numerous canals, and projecting as long spines from 

 the margin. Chalk to present day. Ex. C. calcitrapoides, Chalk. 



Fusulina. Shell fusiform, composed of elongated whorls ; 

 each whorl completely covers the preceding one, and is divided by 

 septa into a number of chambers, which may be again divided into 

 smaller chambers. Adjoining chambers communicate by a slit 

 at the middle of the base of each septum. Septa folded, each 

 consisting of a single layer. Aperture in the form of a fissure. 

 Carboniferous and Permian. Ex. F. cylindrical Carboniferous 

 Limestone. 



Amphistegina. Shell lenticular, with sharp edge ; the upper 

 and lower surfaces unequally convex ; formed of numerous chambers 

 coiled in a plane spiral, each coil almost completely enclosing the 

 preceding one. Septa formed of a single layer. Supplemental 

 skeleton at the centre of the shell. Aperture similar to that of 

 Rotalia. Carboniferous, and Miocene to present day. Ex. A. 

 haueri, Miocene. 



