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NEW YORK STATE MUSEUM 



late and post-Utica age) from the other congeners make it thus 

 strikingly similar to some of the earlier trilobites, as Elliptoce- 

 phala asaphoides Emmons in the series of posterior axial 

 spines ; to Olenellus gilberti; O. fremonti, 

 Eurycare etc. in the genal spines that, especially in the earlier 

 growth stages wander forward along the margin of the free cheeks. 

 Inasmuch as these features are not known of trilobites in the 

 Middle and Upper Cambrian and Lower and Middle Ordovician, it 

 is proper to assume tliat in T. spinosus they are reversional 

 and atavistic in character, using these terms in their popular mean- 

 ing (see below). 





Fig. 12 



Fig. 10 



Fig. II 



Fig. 9 Elliptocephala asaphoides Emmons. Fig. lO 

 Olenellus fremonti Walcolt. Fig. ii O. gilberti Walcott. Fig. I2 

 Paradoxides inflatus Corda. (Figs. 9-1 1 after Walcott, fig. 12 after 

 Barrande 



