The Class Ostracophori 



577 



of the back is overlapped by the posterior dorse-lateral. Pter- 

 ichthyodes milleri from the Lower Devonian, named by Agassiz 

 for Hugh Miller, is the best known species, although numer- 

 ous others, mostly from Scottish quarries, are in the British 



FIG. 361. Cephalaspis dawsoni Lankester. Lower Devonian of Canada. Family 

 Cephalaspidce. (After Woodward.) In the square a portion of the tubercular 

 surface is shown. 



Museum. Asterolepis maximus is a very large species from 

 the same region, known from a single plate. Bothriolepis 

 canadensis is from the Upper Devonian of Scaumenac Bay near 

 Quebec, numerous specimens and fragments finely preserved 

 having been found. 



Microbrachium dicki with the pectoral appendages small 

 occurs in the Devonian of Scotland. 



The earliest remains of Ostracophori are found in Ordovi- 

 cian or Lower Silurian rocks of the Trenton horizon at Canon 



