from the Shales of the Northumberland Coal-field. 377 
dwindled away, and at length entirely disappeared; or rather 
we perceived that they never had had any real existence, and 
that the ‘‘ Minnows and Sticklebacks ” of the Northumberland 
coal-shales have yet to be discovered. 
“Fig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 1. 
Fig. 2. 
Fig. 3. 
EXPLANATION OF THE PLATES, 
PuaTE XIV. 
Sternal plates of Pteroplax cornuta, about half the natural size: 
aa, lateral plates ; 6, posterior portion of central plate appearing 
from beneath the former; ¢, posterior process. 
View of underside of central sternal plate, two-thirds natural 
size: a, perfect lateral wing or lobe; 6, posterior process. 
Premaxilla of Pteroplax cornuta, natural size, the apices of the 
teeth having been restored : a, anterior extremity ; 6, posterior 
articular process; ¢ ec, mucus-grooves; d, external nostril. 
PLATE XV, 
Cranial shield of Pteroplax cornuta, about two-thirds natural 
size: a, frontals; 6, parietals; e, occipitals; d, postfrontals; 
e, epiotics ; f, parietal foramen; g, posterior horns ; /, inner pos- 
terior orbital border. 
Front view of vertebra, three-fourths natural size: a, centrum, 
showing a minute notochordal foramen in the centre; 6, neural 
canal; c, spinous process, restored from another specimen ; 
d, transverse process ; e, anterior zygapophysis. 
Inside view of mandibular ramus of Palgoniscus, showing the row 
of laniary teeth almost perfect, but turned by pressure so as to. 
resent their sides; the row of small exterior teeth is buried 
in the matrix : a, anterior extremity ; 6, posterior articular pro- 
cess; ¢, impressions of the surface-striz in the matrix, a portion 
of the bone having been removed. 
External view of a maxilla of another species of Palzoniscus, 
exhibiting both rows of teeth, the laniary and the small exterior 
teeth appearing to be in the same line, on account of pressure : 
a, anterior extremity; 6, tooth figured in next plate. 
. Inside view of a portion of the alveolar border of the jaw of Pa- 
leoniscus, showing the row of laniary teeth within the small 
exterior row: a, laniary teeth; }, impressions in the matrix of 
the teeth of the exterior row; cc, three of the small exterior 
teeth left adhering to the matrix. 
External view of a mandibular ramus of Acanthodopsis Ward? : 
a, anterior extremity; 6, posterior extremity; ¢, styliform pro- 
cess attached to the dentigerous bone, d. 
PriaTE XVI. 
rn from maxilla of Paleoniscus (Pl. XV. fig. 46): a, enamel- 
P: 
Section of tooth of Paleoniscus, exhibiting the cap of enamel, a; 
6, film of enamel coating the crown, very frequently absent. 
gia of tooth of Pygopterus, from Agassiz, showing the ena- 
mel-tip, a. 
Ann. & Mag. N. Hist. Ser. 4. Vol.i 27 
