190 NEW YORK STATE MUSEUM 



external arch is not a part of the interior segments, then our deter- 

 mination is erroneous. Pulvinulina micheliniana has 

 been found in Arctic waters today and is well known as far back as 

 the Cretaceous, where it is rather common. 



On slide 5 (X) , near Textularia trochus, we find a 

 transverse section which is almost certainly Pulvinulina 

 micheliniana, as it is close to what a cross section of the 

 type would be, the vaulted arch being less symmetrical than 

 Truncatulina refulgens (Montfort) . An excellent diag- 

 onally cut specimen is seen on slide 4 near the spined radiolarian. 



Genus ROTALIA Lamarck 



True Rotaliae form but a small, rather restricted, group as com- 

 pared with Pulvinulina and Truncatulina. They possess true canal 

 systems between the septal partitions and develop a high, turbinoid 

 spire with many chambers. They are, however, often of minute 

 size, and while today Rotalia is abundant in shore deposits of warm 

 and temperate zones, it is known down to 3000 fathoms. When 

 living in favorable shoal waters it is larger and may develop supple- 

 mental skeleton. It possesses minute pores like the nummuline 

 forms, and the walls are of fine calcareous texture. 



Geologically, Rotalia gees back to the lowest Cambrian; but it 

 does not become abu.iiant until Mesozoic time, and is especially 

 prominent in Cretaceous and Tertiary formations. We have one 

 very beautiful and large foraminiferan belonging to this genus, 

 Rotalia orbicularis (d'Orbigny) , which measures 0.38 mm 

 in transverse width. 



Rotalia orbicularis (d'Orbigny) 



Plate 6, figures 9, lo 



Gyroidina orbicularis d'Orbigny, 1826, Ann. Sci. Nat., 7:278, 



no. I, Modele, no. 13 

 Rotalia orbicularis Parker & Jones, 1865, Phil. Trans., 155:389, 



pi. xvi, fig. 34 



Slide 5 (X) shows one of the highest rotaline types of Foraminifera, 

 namely true Rotalia. Rotalia has double septal walls, which are 

 very apparent in the higher magnification (X174) given this cross 

 section. Canal systems are not present in many rotaline genera 

 such as Cristellaria, but become highly specialized in Nonionina 

 Polystomella and Nummulina. We regard the development of 

 Rotalia as most remarkable. Were it not for this canal structure 



