12 



NORTH AMERICAN INDEX FOSSILS. 



XI. Fusulina Fischer. 



Fusiform, laterally elongated and furrowed, coarsely perforate. 

 Chambers subdivided by numerous septa. 



Exceedingly abundant in the Carbonic of North America, Europe 

 and Asia. Carbonic-Permic. 



15. F. secalica (Say). (F. cylindrica Fischer.) (Fig. 18.) Car- 

 bonic. 



Spindle-shaped, with rounded extremities, which generally have 

 the appearance of being slightly twisted. Volutions six to eight 

 and closely coiled. Sometimes one half inch long. 



Widely distributed throughout the Middle and Upper Carbonic. 



XII. Orbitoides d'Ort?igny. 

 Discoidal. Exterior smooth or ornamented with radial striae. 

 Composed of numerous concentric rings, which are divided by trans- 

 verse partitions into small rectangular chambers. A median series 

 of main chambers occurs. Upper Cretacic and Tertiary. 



16. 0. mantelli (Morton). (Fig. 19.) Oligocenic. 

 Discoidal, flattened, thin, thickest at center and tapering from 



there to the sharp margin. Diameter y 2 inch to \y 2 inches. 



Very abundant in the lower Oligocene (Vicksburg) beds through- 

 out the Gulf states, often forming beds of limestone. 



Subclass 2. Radiolaria Muller. 

 The siliceous skeletons of these Protozoa are usually too much 

 broken for identification. In exceptional cases, as in the Miocene 

 of the Barbadoes, they are exceedingly numerous and well pre- 

 served. (Fig. 20.) 



Fig. 20. Radiolaria. a-b (upper left) , Rhopalodictyum marylandicwn ; Cano- 

 spkcera porosissima ; r, IL>xalonche microsphara ; d, Anthocyrtium doronicitm ; e, Can- 

 nartiscus amphicylindricus. All Miocenic (Maryland Geol. Surv. ), much enlarged. 



