70 KINSHIPS OF OSTRACODERMS 
no instance has a trace of endoskeletal parts been ob- 
served. 
The more that is determined of the structural characters _ 
of Ostracoderms, the less is it possible to accept the 
views as to their affinities with forms other than “ fishes,” 
either (Cope) as to their permanent larval-ascidian char- 
acters, or (Patten) as to their relationships with arachnids. 
Their general kinship is certainly to the fishes. Accord- 
ing to Smith Woodward, the markings appearing on the 
visceral surface of head tests indicate the presence of 
gill pouches; in some forms clearly marked furrows sug- 
gest the possession of vertical semicircular canals; fish-like 
sense organs occur (Fig. 77); and their derm plates, in 
their cancellated and bone-like characters, cannot well be 
likened to the exoskeletal parts of invertebrates. 
The lamprey-like form, Pa/gospondylus gunni, Traquair 
(Fig. 73), in the Lower Devonian is by many looked upon 
as the actual solution of the Cyclostome, and even of the 
Ostracoderm puzzle. This interesting fossil was discov- 
ered by Dr. Marcus Gunn, in the Lower Old Red Sand- 
stone of Caithness, and was described in several papers by 
Traquair (Zvans. Edin. Soc., 1892-1894). It is of very — 
small size, commonly of about an inch in length, but is 
admirably preserved (Fig. 73). There can be no doubt 
that Palzeospondylus possessed a ring-like mouth sur- 
rounded by barbels like those of a Myxinoid, and that it 
lacked paired fins. But as a Cyclostome it must have 
highly specialized, having the same relation to the more ~ 
primitive Cyclostomes of its day, as had the minute Acan- 
thodians (p. 81) to the existing sharks.- It had thus a 
remarkably large caudal fin with elaborately bifurcating 
supports; it had evolved stout, ring-like vertebrae, even in 
the caudal region, which had developed stout neural proc- 
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