68 



NORTH AMERICAN INDEX FOSSILS. 



37. H. halli E. & H. (Fig. 102.) Middle Devonic. 

 Broadly turbinate at the base or in young specimens, becoming 



cylindrical in old individuals, frequently with irregular constric- 

 tions showing rejuvenescence. Epitheca strongly wrinkled. 



Abundant in the Hamilton group 

 of New York, Ontario, Ohio,etc, and 

 at the Falls of the Ohio. 



38. H. confluens Hall. (Fig. 103.) 



Middle Devonic. 



Likethe preceding but compound, 

 the corrallites large, and polygonal 

 from crowding. 



In the Hamilton group of New 

 York, Canada, Ohio, etc. 



39. H. tenuiseptatum (Billings). 



Middle Devonic. 



Generally small, more or less cylin- 

 drical, with numerous fine and thin 

 septa, strongly carinated. 



Common in the Hamilton group of New York, Ontario, etc. 



40. H. corniculum (Lesueur). (Fig. 104.) Middle Devonic. 

 Conical and curved at the base, general aspect like Zaphrentis. 



Calyx deep, with steeply sloping sides; broad nearly flat bottom, 

 numerous alternating carinated septa and a well marked fossula. 



Common in Onondaga limestones of New York, Ontario, Indi- 

 ana, etc., and at the Falls of the Ohio. 



Fig. 104. Heliophyllum corni- 

 culum (Ind. Geol. Surv.). 



XVII. Acervularia Schweigger. 

 Coral heads astraeiform, composed of prismatic corallites with 

 numerous septa, the longer of which reach the center. The ap- 

 pearance of an inner wall is caused by crowded dissepiments at the 

 same level. Base of colony covered with a strong peritheca. Sil.- 

 Dev. 



41. A. rugosa (E. & H.). (Fig. 105.) Devonic. 



Corallites from 10 to 15 mm. in diameter, individuals ribbed 

 longitudinally on the exterior and with transversely wrinkled epi- 

 theca. Larger septa meeting and sometimes twisting in the center, 

 carinae moderately developed. 



In the Onondaga beds of Michigan, the Falls of the Ohio, etc. 



