740 
Marvels of the Universe 
front edge and comparatively narrow scaly tail projecting from the middle of its hinder border. 
The body armour of the Sickle-shield consisted of dorsal, ventral and lateral shields separated 
by strips of integument strengthened with a pavement-like coating of close-set scales. 
The 
eyes seem to have been set at the sides of the head, as in the Wing-shield, and the mouth 
probably opened in front of the large ventral shield. 
The structure of the Head-shield, too, suggests that this fish probably crept about the bottom 
FISHES OF THE OLD RED SANDSTONE. 
The Cephalaspis, or ‘‘Head-shield,’’ was in 
all probability a “‘“bottom”’ fish, so that the eyes, 
top of the head, 
would be of service while the remainder of the 
placed close together at the 
fish was buried in the mud. 
and buried itself in sand or muddy sediment. The great 
head-shield, shaped like a saddler’s knife, with its semi- 
circularly rounded margin and acute angles, was curiously 
reminiscent of the head-shield of the trilobites, and the 
eyes were placed close together near its summit, so that 
when the bulk of the fish was buried, the eyes were free 
of sediment, and able to keep watch upon enemies or prey 
passing above in the water. The rest of the body was 
comparatively narrow and was covered with plate-like 
scales ; and the tail, which had smaller scales, carried a 
fin beneath at the tip and another above at the root. 
This creature was apparently coeval with, and about the 
same size as, the more fish-like Wing-shield. The later and 
still stranger form, the Winged Fish, had a scaly, fish-like 
tail, with a terminal fin below, while the main part of the 
body was enveloped in a great buckler composed of large 
overlapping plates, and a composite sub-circular head- 
shield, carrying a pair of dorsal eyes, was somewhat 
sharply marked off in front. Very curious, too, was 
the pair of jointed, limb-like appendages articulated to the 
sides of the body behind the head, which were certainly 
used for locomotion, although their true significance is a 
matter about which there is no unanimity amongst 
zoologists ; some holding that they represent the front 
fins of fishes, others that they are merely movable 
outgrowths of the head-shield, while others think they 
correspond to the  paddle-shaped limbs’ of the 
scorpion-like Euryptermis that lived in those ancient 
seas. 
This raises another very interesting question connected 
with these strange fishes of the Old Red Sandstone. The 
resemblance of the head-shield of the Head-shield to that 
of the trilobites has been already alluded to. It might 
equally well have been compared to that of the king 
crab, an ally of the trilobites. The 
these ancient fishes and the still more ancient 
likeness, indeed, 
between 
trilobites and contemporaneous king crabs, which were related both to the crustaceans and the 
arachnids, is too striking to be disputed ; but while most authors hold that the likeness is purely 
superficial and due to adaptive converget.ce, there are others who consider it to be an outward and 
visible sign of inward and genuine kinship, and who see in these ambiguous creatures actual links 
in a chain of affinity between the vertebrated and the articulated animals, pointing to the descent 
even of man himself from species more nearly related to king crabs and scorpions than to any 
other living animals. 
