OSTRACODERM FISH IS. 



53 



near the hind end of the lateral plate on each side. The covering 

 of the front part of the tail consists of closely-set rhombic scales. 

 Remains of Pteraspis occur in the Lower Old Red Sandstone of 

 England and Scotland, and the Lower Devonian of Galicia. 



The models of Vrepanaspis gemilndenensis (162 and 163 ; see 

 also fig. 30) are of the natural size, and are based on the results 

 of extensive investigations conducted by Dr. R. H. Traquair. The 

 head and trunk region is broad, depressed, and sharply marked 

 off from the tail, which is short, and terminates in a high caudal 

 fin provided wfth stout marginal scales (fulcra) on its upper and 

 lower edges. The median shields of the dorsal and ventral 



Fig. 30. — Restoration of Drepanasjpis (/einiindenensts. 



A, upper view; B, lower view. (After R. II. Traquair.) 



surfaces are relatively smaller than in Pteraspis, and are bounded 



by a mosaic of small plates. The remains of Drepanaspis occur 



in the Lower Devonian rocks of Gemiinden, in Germany. 



The model of Cephalaspis (164) is enlarged three times (linear). 

 In Cephalaspis the eyes are large and fairly close together ; there is 

 median dorsal fin and a heterocercal tail. The head-shield of 

 Cephalaspis is large, rounded in front, and with a moderately- 

 sharp edge. The angles of the head-shield are produced backward, 



Drepan- 

 aspis. 



Cephal- 

 aspis. 



