FISHES CHAP. 
Fic. 312.—Restoration of Palaeo- 
spondylus. he figure shows 
the ventral surface of the skull 
and a lateral view of the ver- 
tebral column. cc, Calcified 
cirri ; p.a, auditory capsule ; 
t.p, nasal capsule (7); ~, post- 
occipital plate. (From Parker 
and Haswell, after Traquair.) 
of limbs, limb-girdles, jaws, or branchial 
arches, nor any evidence of the existence 
of scales, denticles, or other exoskeletal 
structures. 
Palaeospondylus has been regarded 
as a Cyclostome, a view which derives 
its principal support from the resem- 
blance of the cirri-encireled orifice at 
the anterior end of the skull to an 
unpaired nasal or naso-pituitary aper- 
ture, and perhaps some measure of 
credence from such purely negative 
evidence as the apparent want of limbs, 
and of any structures comparable to 
jaws. But even if it be admitted that 
there is some reason for this view, it 
is certain that Palaeospondylus obtained 
a far higher grade of specialisation in 
certain respects than any of the exist- 
ing Cyclostomata ; the presence of calci- 
fied vertebral centra and neural arches 
is conclusive on this point.’ Palaeo- 
spondylus has also been compared with 
a larval Arthrodiran and with a larval 
Dipnoid.” 
II. Ostracodermi. 
The Palaeozoic fish-like forms, which, 
more as a matter of convenience than 
as an expression of real kinship, it 
has been customary to include in this 
group, are amongst the earhest Craniates 
of which we have any precise knowledge. 
' In a recently published and important con- 
tribution to our knowledge of Palaeospondylus, by 
Professor and Miss Sollas (Phil. Trans. 196, 1903, 
p- 343), they describe structures on the ventral 
surface of the head, which they maintain to be branchial arches, as well as others. 
which, in their view, may represent hyomandibular and mandibular elements. 
* Graham Kerr, Proc. Camb. Phil. Soc. x. 1900, p. 298, 
