The crest on the otherwise flattened supraoccipital of 

 triacanthodins is best developed in Triacanthodes and 

 Johnsonina, being high and relatively wide at the 

 anterior edge, while in all the other genera the crest is low 

 and thin. Other features of the anatomical diversity of 

 the triacanthodids are discussed by Tyler (1968), and for 

 the muscles by Winterbottom (1974). 



Generic relationships. — Parahollardia and Hollardia 

 are obviously very closely related, with the former slight- 

 ly the more generalized of the two, based on the evidence 

 of its retention of a series of teeth internal to the major 



