552 NORTH AMERICAN INDEX FOSSILS. 



Lower Chico of California and Lower California. 



CLI. Radiolites Lamarck. 



Lower valve conical, erect, elongated, vertically ribbed or made 

 up of successive layers ; usually with two, somewhat smooth bands 

 extending from the apex to the upper margin, probably marking 

 the position of the siphon openings. Outer layer very thick, com- 

 posed of large, polygonal cells or hollow prisms. Upper valve 



Fig. 756. Radiolites texanus, large valve. ( After Roemer. ) 

 Fig. 757. Radiolites texanus, section enlarged. (After Roemer. 



