THE STATE GEOLOGIST. 



41 



Pig. 2. 



Cephalaspis murchisoni Egert. Silurian and Lower Devonian; Hereford- 

 shire. Lateral aspect, restored by Dr. A. S. Woodward. X %• 



Fig- 3- 



Pteraspis rosirata Ag. Lower Old Red Sandstone; Great Britain, 

 view of partially restored fish. X Z A- 



Side 



TremataspiSj together with the remarkable forms described with- 

 in recent years from the Scottish Silurian, grouped by Dr. Tra- 

 quair under the name of Anaspida. Of the above mentioned 

 forms, only the genus Cephalaspis appears to have been common 

 to both Europe and America. 



Another primitive group of organisms found in association 

 with Ostracophores in the Devonian of various parts of the 

 world, and by many regarded as more or less akin to them, has 

 received the name of Arthrodires, in allusion to a curious hinge- 

 like device by which the body armor is movably united with the 

 head-shield. Arthrodires are heavily armored fish-like verte- 

 brates, the head and forward portion of the body being encased 

 in a system of dermal plates, usually ornamented with fine stellate 

 tubercles, and with cartilaginous axial skeleton. No indications 

 have been found of paired fins, properly speaking, but a lower 

 jaw occurs, suspended freely in the soft parts without being artic- 

 ulated to the cranium. 



The typical genus is Coccosteus (Fig. 4), a comparatively small 

 form, common to both sides of the Atlantic, and ancestral to the 



