from the Shales of the Northuniberland 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. 



EXPLANATION OF THE PLATES. 

 Plate XIV. 



Fig. 1. Sternal plates of Pteroplax cornuta, about half the natural size : 

 a a, lateral plates ; b, posterior portion of central plate appearing 

 from beneath the former ; c, posterior process. 



Fig. 2. View of underside of central sternal plate, two-thirds natural 

 size : a, perfect lateral wing or lobe ; b, posterior process. 



Fig. 3. Prfemaxilla of Pteroj^lax cornuta, natm-al size, the apices of the 

 teeth having been restored : a, anterior extremity ; b, posterior 

 articular process ; c c, mucus-grooves ; d, external nostril. 



Plate XV. 



Fig. 1. Cranial shield of Pleroplax cornuta, about two-thirds natural 

 size : a, frontals ; b, parietals ; c, occipitals ; d, postfrontals ; 

 e, epiotics ; /, parietal foramen ; g, posterior horns ; h, inner pos- 

 terior orbital border. 



Fig. 2. Front view of vertebra, three-fourths natural size : a, centrum, 

 showing a minute notochordal foramen in the centre ; b, neural 

 canal; c, spinous process, restored from another specimen j 

 d, transverse process ; e, anterior zygapophysis. 



Fig. 3. Inside view of mandibular ramus of Palisoniscus, showing the row 

 of laniary teeth almost perfect, but turned by pressure so as to 

 present their sides ; the row of small exterior teeth is buried 

 in the matrix : a, anterior extremity ; b, posterior articular pro- 

 cess ; c, impressions of the surface-striae in the matrix, a portion 

 of the bone having been removed. 



Fig. 4. External view of a maxilla of another species of Palceaniscus, 

 exhibiting both rows of teeth, the laniary and the small exterior 

 teeth appearing to be in the same line, on account of px-essure : 

 a, anterior extremity ; b, tooth figured in next plate. 



Fig. 5, Inside view of a portion of the alveolar border of the jaw of Pa- 

 Id'oniscus, showing the row of laniary teeth within the small 

 exterior row : a, laniary teeth ; b, impressions in the matrix of 

 the teeth of the exterior row ; c c, three of the small exterior 

 teeth left adhering to the matrix. 



Fig. 6, External view of a mandibular ramus of Acanthodopsis Wardi-. 



a, anterior extremity ; 6, posterior extremity ; c, styliform pro- 

 cess attached to the dentigerous bone, d. 



Plate XVI. 



Fig. 1. Tooth from maxiUa of Palceoniscm (PL XV. fig. 4 b) : a, enamel- 

 tip. 

 Fig. 2. Section of tooth of Palceoniscus, exhibiting the cap of enamel, a ; 



b, film of enamel coating the crown, very frequently absent. 

 Fig. 3, Section of tooth of Pygop)terus, from Agassiz, showing the ena- 

 mel-tip, a, 



Ann. & Mag. N. Hist. Ser.4. Vol.i. 27 



