FAMILY 34. AMPHISTEGINIDAE 281 



aperture typically ventral, a slightly arched opening, the area 

 adjacent to the aperture papillate. 



Genus ASTERIGERINA d'Orbigny, 1839 

 Plate 42, figure 1 ; plate 44, figure 4 



Genotype, by designation, Asterigerina carinata d'Orbigny 

 Asterigerma d'Orbigny, Voy. Amer. Merid., vol. 5, pt. 5, 1839, "Foram- 

 iniferes", p. 55. 



Test trochoid, biconvex, the ventral side usually more strongly 

 so than the dorsal, dorsal side v^ith the chambers appearing 

 regularly coiled, on the ventral side w^ith angular supplementary 

 chambers coming in betv^een the regular series, large and 

 regularly rhomboid in shape ; sutures on the dorsal side a simple 

 curve; aperture on the ventral side at the base of the chamber 

 margin. 



Eocene to Recent. 



Genus AMPHISTEGINA d'Orbigny, 1826 



Plate 42, figures 2, 3; plate 44, figure 5 



Genotype, by designation, Amjjhistegina lessonii d'Orbigny 

 Aniphistegma d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 304. 

 Omphalophactis Ehrenberg, Abhandl. k. Akad. Wiss. Berlin, 1838, p. 132 

 (genoholotype, Omphalophacus hemprichii Ehrenberg). 



Test usually lenticular, trochoid, often involute on the dorsal 

 side in the adult; supplementary chambers more or less irreg- 

 ularly rhomboid ; sutures and chambers with a pronounced angle, 

 no true secondary canal system developed ; aperture small, 

 ventral, the wall granular about the opening. 



Tertiary to Recent. Carboniferous ( ?) 



These two genera with their supplementary chambers on the 

 ventral side are derived along a line from Eponides. The aper- 

 ture is typically that of the Rotaliidae, and it is evident from a 

 study of the structure that Asterigerina is very closely allied to 

 Amphistegina, and that the two should be grouped together. 

 Amphistegina has little in common with the Nummulitidae where 

 it has usually been placed. There are records of Am-phistegina 

 from the Palaeozoic but they are not wholly satisfactory and 

 probably represent some other genus. 



