960 



CLASS PISCES. 



Family Pteraspidid^. — The entire body in this family is un- 

 known • but the dorsal shield (figs. 886, 887) is usually composed 

 of several pieces united together, and has its borders thickened and 



Fig. 886. — Imperfect dorsal 

 shield of Cyathaspis Banksi; 

 from the Silurian of Ludlow. 

 (After Murchison.) 



Fig. 887. — Dorsal shield of 

 Pteraspis rostrata ', from the 

 Lower Devonian of Hereford. 

 Reduced. (After Lankester.) 



bent, and in structure approaches the scales of Teleostean Fishes. 

 It has a median posterior spine, and sometimes small lateral cornua. 

 There is also a small shield on the ventral aspect of the fish, 

 which, like the dorsal one, is marked by fine striations. In the 

 type genus Pteraspis, the dorsal shield (fig. 887) is shaped like 

 an arrow-head, and composed of seven pieces ; while in Cyath- 

 aspis (fig. 886) it is oval, composed of only four elements, and has 

 the posterior spine very short. Scaphaspis has been founded on 



Fig. 888. — Reduced restoration of Pteraspis. 



remains belonging to these two genera, which are found in both 

 the Silurian and Devonian ; the simple shields described under this 

 name having apparently been placed ventrally beneath the more 

 complex ones, on the evidence of which the other genera were 



