Aatroooenia decaturensis , sp. hot. 
PI. fig. 
Coral luia massive, rather lagge, upper surface with numerous 
gibbosities. One speoimen has a base 14 by 17 cm, respectively 
as the smaller and greater diameter, and is about 8 cm. in height, 
another has 19 cm. as the greatest diameter of the base. 
Corallites polygonal, separated by walls that are never 
very thick, rarely as much as 1 Em., upper edge usually if not 
always marked by a small raised, granulated line. The distal 
ends of the septa are produced as short oostae to this line and 
quite often a granulation occurs between each pair of costae. 
The diameter of the corallites varies from 1.5 to 2.5 mm., about 
2 mm. is the average. Calices shallow* 
Septa distant, formally sixteen in number, of which eight 
extend to the columella, occasionally twenty, with ten reaching 
the columella. Their outer ends are slightly prominent on the 
wall, and are equal in size 
The ihner margins lie almost in a 
