of Amphicentram granulosuni. 281 



EXPLANATION OF PLATE IX. 



In all the figures the same bones are denominated by the same letters. 

 f, frontal ; p, parietal ; sq, squamosal ; p.f, posterior frontal ; a.f, anterior 

 frontal ; n, nasal ; p.mx, premaxillary ; mx, maxillary ; d, dentary of 

 inaudible ; sp, splenial, or internal dentary of mandible ; pa, palato- 

 pterygoid ; hm, hyomandibular ; op, operculum ; s.op, suboperculum ; 

 p.op, praeoperculum ; br } branchiostegal rays ; s.o, suborbitals ; sr.o, supra- 

 orbitals ; s.cl, supraclavicular (scapular, Owen) ; cl, clavicle (coracoid, 

 Owen); i.cl, interclavicular. 



Fig. 1. Head of Amphicentrum gramdosum, natural size. The edentulous 

 edge of the maxilla is shown, though posteriorly in impression 

 only ; and a portion of the middle of the bone being broken 

 out, the outer denticulated ridge of the more deeply placed 

 palatopterygoid is uncovered. The edentulous margin of the 

 dentary of the mandible is shown at its fore part ; posteriorly it 

 is also broken away, and the denticulated ridge of the spleuial 

 element has been exposed, by digging away the matrix with a 

 sharp instrument. 



Fig. 2. Counterpart of the same specimen, showing the contour and the 

 sculpturing of the maxilla in impression ; the edentulous margin, 

 completely shown in the former figure, is a little injured in front. 

 The edentulous margin of the dentary of the mandible, forming 

 a ridge external to the dentigerous one of the splenial, is seen 

 for the greater part of its length, partly in impression. 



Fig. 3 is taken from a plaster mould or impression of a head contained 

 in a hard ironstone nodule. In this specimen the cheek was 

 broken away, so as to expose the outer surface of the palate, 

 and the mandible was split through longitudinally. By soften- 

 ing what remained of the bone of these parts with dilute acid, 

 and then carefully picking and brushing it away from the hard 

 ironstone matrix, a perfect impression of the inner aspect of the 

 palate, hyomandibular, and mandible was obtained, the con- 

 figuration and relations of these parts being therefore accurately 

 reproducible in an impression taken from the preparation thus 

 made. Compare the palatopterygoid and mandible thus ex- 

 hibited in situ with the detached bones represented in figures 5, 

 8, and 9. 



Fig. 4. View of a crushed head of Amphicentrum, showing, seen from the 

 internal aspect, the edentulous oral margin of the maxilla, both 

 dentigerous ridges of the palatopterygoid, the beak-like pras- 

 maxilla, and the somewhat similarly shaped anterior extremity 

 of the dentary of the mandible, as well as the ridges of the 

 splenial or internal dentary of the latter. 



Fig. -5. Inner aspect of the internal dentary of the right mandible, taken 

 from the same specimen figured by Dr. Young as " maxilla." En- 

 larged one half. 



Fig. 0. Another specimen of the same bone, seen from the inner or oral 

 side, natural size. 



Fig. 7. The same specimen, seen from the outer side. 



Fig. 8. The same specimen, seen from above. 



Figs. 9 & 10. Two specimens of the palatopterygoid, seen from the oral 

 aspect, natural size. In fig. 9 the posterior-superior thin expan- 

 sion is broken off; and in fig. 10 the process descending behind 

 to the articulation of the lower jaw is deficient, and indicated 

 by dotted lines. 



