REMAINS OF REPTILES AND FISHES. 119 



Fig. 3. Prsemaxilla of Pteroplax cornuta, natural size, the apices of the 

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

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



PLATE II. 



Fig. 1. Cranial shield of Pteroplax cornuta, about two-thirds natural size' 

 a, f rentals ; 6, parietals ; c, occipitals ; d, postfrontals ; e, epio- 

 tics ; y, parietal foramen ; g, posterior horns ; h, inner posterior 

 orbital border. 



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

 showing a minute uotochordal foramen in the centre ; b, neutral 

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

 transverse process ; e, anterior zygapophysis. 



Fig. 3. Inside view of mandibular ramus of Palaoniscus, 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, impi-essions of the surface-striaj in the matrix, a portion 

 of the bone having been removed. 



Fig. 4. External view of a maxilla of another species of Palceoniscus, ex- 

 hibiting 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 ; b, tooth figured in the next Plate. 



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

 Iceoniscus, showing the row of laniary teeth within the small ex- 

 terior row ; a, laniary teeth ; 6, 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 ; b, posterior extremity ; c, styliform pro- 

 cess attached to the dentigerous bone, d. 



PLATE III. 



Fig. 1. Tooth from maxilla of PaIceo7iiscus (Plate II., fig. 4 b) : 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 Pygopterus, from Agassiz, showing the enamel* 



tip, a. 



