8 
POPULAR SCIENCE REVIEW. 
Cephalaspis — we shall see that specimens have been found 
showing the entire body, they prove, though only by negative 
evidence, that such a structure did not exist. 
This oldest form of fish is widely spread; specimens of 
Scaphaspis having been obtained from Upper Silurian and 
Lowest Devonian rocks in Gallicia, Russia: from the Lower 
Devonian, Eifel ; from the Lower Devonian, Mudstone Bay, S. 
Devon ; from Polperro, Cornwall ; from the Lower and Upper 
Ludlow, the Downton sandstone, and the Lower Old Red 
Sandstone of Worcester, Hereford, and Shropshire; and from 
the Old Red of Forfarshire, Scotland. In all seven species have 
been described and figured. 
Fig. 5. 
Fig. 4. 
DIAGRAM OF THE SHIELD OF DIAGRAM OF THE SHIELD OF] 
Cyathaspis (after Lankester). Pteraspis (after Lankester). 
o. orbits, c. cornua. (Letters as in Figs. 3 and 4). 
d. r. s. as in Fig. 3 of Scaphaspis. 
Although the shield in Cyathaspis (Woodcut, Fig. 4), is as 
simple in outline as in Scaphaspis , yet it betrays a tendency 
towards a more complex structure, being divided by sutures 
into a frontal or “rostral” portion, two lateral pieces (called 
“cornua”) and a central or “discal” region. It is represented 
by two species only, from the Downton sandstone, and the 
Lowei Old Red (or “ Cornstones ”) of Herefordshire. 
A new genus, named Iiolaspis , represented by a head-shield 
without sutures, from the Lower Old Red (“Cornstones”) of 
Abergavenny, Monmouthshire, has lately been described and 
figured,* but although considered by Professor Lankester to be 
* " Geol. Mag.” 1873, vol. x. p. 241, plate x. 
