56 



NORTH AMERICAN INDEX FOSSILS. 



4. S. (Enter olasraa) caliculum Hall. (Fig. 76, g y 77.) Middle 

 Siluric. 



Small, slender, uniformly tapering corals with moderately deep 

 cup, and comparatively few (20-50) septa separated by twice their 

 width, and epitheca thin, showing costal 

 grooves. Septal ends unite into a reticu- 

 late pseudo-columella. 



Niagara beds of New York, Canada, etc. 



5. S. (Stereolasma) rectum Hall. (Fig. 78, 

 79.) Middle Devonic. 

 Generally larger and more robust than 



preceding, with strongly wrinkled and often 

 irregular surface, owing to strong epitheca. 

 Septa comparatively few, uniting at the cen- 

 ter. A well marked fossula is present. 

 Hamilton group of NewYork,etc. 



Fig. 79. Stereolasma 

 rectum, transverse and 

 longitudinal sections (af- 

 ter Simpson). 



II. Zaphrentis Rafinesque. 



Simple, conical or turbinate corals, becom- 

 ing conico-cylindrical in some large species. 



Calyx deep, with well developed septa, the primary ones gener- 

 ally reaching to the center. 

 Dissepiments and tabulae oc- 

 cur, the latter usually well 

 developed and bent down- 

 wards at the periphery. A 

 deep fossula marks the abor- 

 tion of the cardinal septum. 

 Epitheca thin. Sil.-Carb. 



6. Z. gigantea Lesueur. 

 (Fig. 80.) Middle Devonic. 

 Generally of large size be- 

 coming cylindrical in the 

 adult. Length sometimes 2^ 

 feet with a diameter of three 

 inches. Bottom of calyx 

 often shows a tabulum, the 

 septa not reaching the cen- 

 ^ „ Ml ' . . . .. ,. , ter. Fossula large and deep. 



FlG. 80. Zaphrentis gigantea, longitudinal " r 



and transverse sections (Lambe). Epitheca strongly wrinkled. 



