18 



Fossil Fishes, 



Table-case, 

 No. 35. 



Group III. — Cephalaspid^:. 



The Cephalaspidce includes a peculiar and very ancient group 

 of Palaeozoic fishes, limited to the Upper Silurian and Old Red 

 Sandstone. 



•/.'. 



Fig. 3$.— Pteraspis (restored), side view (after Lankester), Lower Old Red Sandstone, 



Herefordshire. 



The earliest (Scaphaspis ludensis) is from the Lower Ludlow 

 rock, near Ludlow, the oldest known fish. The head is covered 

 with a large buckler composed of one or more pieces, a tail covered 



Fig. 39. —Restoration of shield of Pteraspis, upper aspect (after Lankester), Lower Old 



Red Sandstone, Herefordshire. 



Fig. 40.— Cephalaspis Lyelli (restored), side-view (after Lankester), Old Red Sandstone, 

 Forfarshire (drawn about one-third uatural size). 



with rhombic scales ; but no internal skeleton of any kind has been 

 met with. 



They are divided into two groups ; Meter ostraei, which have no 

 bone-cells in their shields, viz. : — Scaphaspis, Pteraspis (Figs. 38, 

 39), and Cyathaspis : and Osteostraci, viz. : — Cephalaspis, Auchen- 

 aspis, and Fiikeraspis, in which bone-cells are present. Recent 

 discoveries render it doubtful whether, in the Heterostraei, the 

 genera Scaphaspis and Pteraspis are distinct; the first is perhaps 

 the ventral shield of the second. 



