138 Proceedings of the Boy al Physical Society. 



iiifradcntary ; and there is also some evidence of a fourth 

 small plate on the lower margin of the jaw, separating here 

 the angular from the first infradentary for a little distance.* 



In another specimen, compressed vertically and showing 

 the top of the head, both maxillcT- are seen, forming the upper 

 margin of the mouth, while, forming its lower margin, both 

 dentaries are seen on the edge of the nodule, here retaining 

 their bony substance and external sculpture. Their contour 

 proves beyond a doubt that the dentary element of the mandi- 

 ble of Ehizodopsis is undistinguishable from the bone hitherto 

 reckoned as prsemaxilla, but which I have already shown 

 cannot possibly be so. The very same thing is most clearly 

 shown in a shale specimen belonging to Mr Plant of Salford, 

 in which a vertically compressed head is seen from below ; so 

 that I have no hesitation in affirming the identity of the bones 

 in question. 



Here, however, an objection to this view may be raised. 

 The mandible of Ehizodopsis when perfect, as in most of the 

 specimens from Fenton now before me, shows not merely one 

 large tooth in front, but two or three additional ones behind it 

 and internal to the series of small teeth, though, as stated by 

 Messrs Hancock and Atthey, these additional larger teeth "are 

 seldom present." What has become of these in the detached 

 dentary, if such be the real nature of the reputed praemaxilla? 



A ready explanation of this is found in the structure of the 

 lower jaw of certain Old Eed Sandstone " Dendrodonts," in 

 which the laniary teeth are not attached to the dentary bone 

 proper, but to a series of accessory " internal dentary " pieces 

 articulated to its inner side.-f* Should this be also the case 

 with the posterior laniaries of the mandible of Ehizodopsis, 

 then, in cases where its elements are broken up and separated, 



* That these sutures on the outer surface of the mandible in Ehizodopsis 

 have not been previously observed is fully accounted for by the difficulty of 

 tracing the line of demarcation between constituent and closely united osseous 

 elements, in cases where' we have to deal with a granulated or otherwise orna- 

 mented external bony surface. Such, lines of demarcation are more easily 

 determined where the bones are seen from the inner surface, or where a sharp 

 cast in hard ironstone of that inner surface has been preserved. 



t See Pander's ''Saurodipterinen, Dendrodonten, etc., des devonischen 

 Systems," pp. 41-43, tab. x., figs. 2, 3, 4, 14, 22. 



