CEPHALASPID2E. 
187 
oblong portions, the areas immediately within this are at least as 
long as broad, while those forming the greater part of the “ flap ” are 
considerably broader than long, and are suggestive of a certain 
amount of flexibility in the original structure, The piecise outline 
of the extension is not determinable, but it evidently tapers pos¬ 
teriorly, and its extreme length is nearly equal to half the length of 
the shield. 
Appendages of the character just described have already been 
noticed by Powrie and Lankester, and, in the absence of satisfactory 
evidence as to their connections, they have naturally been regarded 
as pectoral fins. It now appears, however, that the structures are 
merely a portion of the shield itself, divested ot the outei and mnei 
layers to ensure flexibility. The arrangement and peculiarities of 
the compound plates have, indeed, suggested to Prof. Lankester that 
these appendages “ may have had other functions than that of mere 
locomotion and he adds, as not improbable, “ that they may have 
been efficient in causing currents of water to pass to the branchial 
organs covered in by the great head-shield (whose outlets are indi¬ 
cated by the lateral perforation in the shield of Pteraspis), and have 
thus aided respiration as well as locomotion, as is observed in the 
fry of Teleostean fishes at the present day with regard to the pectoral 
fin.” Some connection with the gills has thus already been suspected, 
and it now seems most probable that the appendages in question 
actually correspond to a pair of opercula, and may henceforth be 
designated as such. 
The inferior surface of the head is only shown in part by one fossil, 
and the structures are not sufficiently complete to give any clue as 
to the characters of the mouth. At least posteriorly, the skin is 
supported by thin and delicate polygonal plates, closely fitted to¬ 
gether (see PI. X. fig. 2). 
As in the more typical members of the genus Cephalaspis , the por¬ 
tion of trunk behind the shield is trihedral in form, gradually tapering 
towards the caudal extremity, and having a segmented appearance, 
owing to the shape and arrangement of the scutes. As shown dis¬ 
tinctly by one specimen (PI. X. fig. 4) and less distinctly by others, 
the inferior surface is formed by a single paired series of elongated 
scutes (v.), each broadest at its outer extremity and gradually nar¬ 
rowing while directed forwards mesially. A series of small scutes 
corresponding in number, and forming a kind of fringe, is arranged 
along the inferior lateral angle (Z.) of both sides. Each of these is 
onlv connected with the one in front and behind at its base, and the 
outer free extremity is directed backwards, while the anterior 
margin is gently rounded and serrated. Again of equal number, and 
having bevelled ends articulating with the inferior marginals just 
