PORIFERA. 19 



The characteristic fossil throughout the lead region, of the 

 Galena limestone in Illinois, Iowa and Wisconsin. 



Fig. 28. Receplaculites oweni (Minn. Geol. Surv., Schuchert & Winchell). 



10. R. hemisphericus Hall. Siluric. 

 Small, rarely exceeding two inches in diameter. Hemispherical 



or subglobular with truncated base. Cells in rows obliquely 

 radiating from a sub-central point, minute near point of origin but 

 rapidly increasing in size over the upper surface and again decreas- 

 ing down the sides. 

 Niagara of Wisconsin. 



11. R. ohioensis Hall & Whitfield. (Fig. 29.) Siluric. 

 Differs from R. hemisphericus in its smaller size, not exceeding 



one and one fourth inches in diameter, and in its smaller cells. 



Niagara of Ohio. 



1 2. R. mamillaris Walcott. Ordovicic. 

 Usually in form of an inverted cone with 

 a deep depression above. In more ex- 

 panded forms the center of the otherwise 

 broadly rounded base extends as a short- 



FlG. 29. Receptaculites . . , • .. 



,. . * r \ c . pointed projection. 



ohioensis (Ohio Geol. burv. ). L L J 



In upper portion of the Pogonip group 

 (= Chazy) in Nevada. 



13. R. (Ischadites) iowensis (Owen). (Fig. 30.) Ordovicic. 



Base concave, upper surface, flatly dome-shaped, with an open- 

 ing into the hollow cavity. Small rhomboidal cells opening on 

 surface in curved rows, intersecting in arches. 



Galena limestone of Iowa, Wisconsin and Minnesota. 



