﻿CEPHALASPID.E. 179 



pair of great rounded lobes, meeting in the middle line, is con- 

 spicuous in advance of the orbital region. As shown from beneath 

 (fig. 19), the margin of the shield is reflexed inwards to form a 

 flattened and ornamented inferior rim, wider behind than in front ; 

 and, as proved by transverse sections (fig. 20), the inner border of 



Cephalaspis. — Transverse section of shield, after Lankester. 

 i, inferior lamina ; m, margin ; s, superior lamina. 



this rim is continued upwards into a delicate smooth lamina of cal- 

 cified tissue (i.), which lies beneath the outer or superior lamina (s.) 

 of the shield proper. 



Cephalaspis lyelli, Agassiz. 



1835. Cephalaspis lyellii, L. Agassiz, Poiss. Foss. vol. ii. pt. i. p. 142, 



pi. i. a. fig. 2 (non fig. 1), pi. i. b. figs. 3, 4 {non figs. 1, 2, ? 5). 

 1839. Cephalaspis lyellii, R. I. Murchison, Silur. System, p. 589, pi. i, 



figs. 2, 3 {non fig. 1). 

 1870. Eucephalaspis lyellii, E. R. Lankester, Fishes Old Red Sandst. 



pt. i. (Pal. Soc), p. 43, pi. viii. fig. 1, pi. xi. figs. 1, 2. 

 1870. Eucephalaspis agassizii, E. R. Lankester, ibid, p, 46, pi. ix. figs, 



2, 3, 6, and woodc. fig. 18. 



Type. Head and trunk, wanting fins ; British Museum. 



The type species, of moderate size. Shield sharply rounded or 

 obtusely pointed in front; orbits placed nearly midway between 

 the anterior and posterior margins ; cornua well developed, broad, 

 and acutely pointed. Superficial tuberculations relatively small, 

 closely and irregularly arranged. Scaly trunk about two and a half 

 times as long as the shield. 



Form. Sf Loc. Lower Old Red Sandstone : Forfarshire, Hereford- 

 shire, Monmouthshire, and Worcestershire. 



The English shields originally placed by Agassiz in C. lyelli were 

 separated from this species by E. R. Lankester under the name of 

 C. agassizi, from the circumstance that " the orbits in the Scotch 

 specimens are placed more posteriorly in tne shield, and the cornua 



n2 



