582 WARREN S. SMITH 



forms ranged from two to three inches in length. Naturally, 

 smaller forms have been noted, as in Grabau and Shimer, Index 

 Fossils, p. 295, where one and one-fourth inches is given as the 

 entire length. 



Fig. 12, A is the front, Fig. 12, B the top, and Fig. 12, C the side 

 view of the one specimen. The dotted line in Fig. 12, B gives the 

 outline of the eye, which was destroyed in uncovering the fossil. 



Both of these forms are index fossils of Trenton age. Naturally, 

 they are not restricted to one bed, but in no case have they been 

 recorded as younger than Ordovician. 



The writer is indebted to Dr. Shimer and to Dr. Grabau for 

 valuable help and advice. 



