102 



NORTH AMERICAN INDEX FOSSILS. 



die of each broad face, converge and unite downward, while those 

 on either side become broader. Surface rough with granules. 

 Columella papillose. 



In the Claibornian group of South Carolina, Alabama, Missis- 

 sippi and Texas. 



LV. Discotrochus Milne-Edwards & Haime. 



Free, disk-like corals, with a flat base and slightly arched upper 

 surface. Septa carinate, radial, the longer joining the papillose 

 columella. Costae simple. Tertiary. 

 137. D. orbignianus E. & H. (Fig. 166.) Eocenic. 



Base with the large unequal costae becoming indistinct near the 

 concave center. Diameter 6 mm., height 1.5 mm. 



FlG. 165. Platytrochus stokesi (after Fir,. 1 66. DiscotrocJnis orbignianus, 

 Vaughan, enlarged). with partial enlargement (after Vaughan). 



In the Lower Claibornian of Alabama, Mississippi, Louisiana 

 and Texas. 



LVI. Tukbinolia Lamarck. 



Small, free, conical corals with a circular calyx. Septa prolonged 

 externally into strong costae. Septa in several cycles. Alternate 

 septa triple from union with smaller ones, 

 columella well developed. Tert.-Recent. 



138. T. pharetra Lea. (Fig. 167.) Eocenic. 

 Twenty-four rounded and prominent costae, 

 with entire margins, twelve of which become 

 larger basally and only six occurring at the 

 base. A double row of pores occurs in the 

 furrows between the costae. Columella 

 slightly projecting in the form of a star, with 

 six rays, each of which fuses with a principal Fia l6 J' Tttr ^' a 



pharetra (after Vaugh- 

 Se P tum - an, enlarged). 



