176 ]SIK. T. ATTHET OX PTEKOPLAX COENUTA. 



are placed at about equal distances fi-om each other. On not one 

 of these mandibles do I find the slightest indication of a suture 

 which might divide the bones bearing the laniary teeth. 



If, as the author of the above-named paper states, our prae- 

 maxilla is the alveolar border or dentary piece of the mandible 

 detached from that bone, how does it happen that in all the large 

 series of mandibles of Rhizodopsis in my collection the alveolar 

 border or dentary piece with teeth, which is supposed to repre- 

 sent our prsemaxilla, is not wanting in any specimen, whilst the 

 pra?maxilla, which is much more common in our coal-field than 

 either the maxilla or the mandible, is absent fi'om a good many 

 of the more perfect specimens of Rhizodopsis (which is, from the 

 lax connexion of this bone with the cranium, what might have 

 been expected) ? 



Of the largest specimen the maxillnc measures 1*4 inch in 

 length; their upper margins are injured; the lower, bearing the 

 row of small teeth, are intact. Tlie praemaxilla?, articulating 

 with the front of the maxilla), unite together on the median line, 

 forming the fore part of the mouth below the snout ; each bone 

 is 1-6 in length and 0*2 inch in height next the symphysis, gra- 

 dually diminishing backwards. 



That we have here the real procmaxilla is beyond a doubt. 



X. — On Ptcroplax Cornuia, H. and A. By Thomas Atthet. 

 With two Plates by William Dintjixg. 



In the "Annals and Magazine of Natural Histoiy," Ser. 4, Vol. 

 I., 1868, appeared " Notes on the Remains of some Reptiles and 

 Fishes from the Shales of the Northumberland Coal-field," by 

 my late friend Mr. Albany Hancock and myself. 



In those notes were descnbed two crania of Pteroplax cornuia, 

 the upper surface of the smaller one being figured of about two- 

 thirds the natural size (Plate XV., fig. 1) ; subsequently the mat- 

 rix liaving been more carefiillv removed from the surfaces of botli 



