294 Mr. D. M. S. Watson on 



purple and green cornstoiie mucli resembling some of those 

 found in the Herefordshire Old Red Sandstone. This matrix 

 is comparatively easily removed, and Prof. Seeley cleared 

 the Avhole left temporal fossa and orbital cavity and part of 

 the palate. I have recently further developed the specimen, 

 removing the matrix surrounding the base and back oL" the 

 skull and exposing the teeth, the right quadrate, and the 

 posterior part of the right side of the brain-case. 



This very complete development, vpitli the fact that almost 

 all the sutures are clearly shown, enables me to correct 

 some accepted statements and determinations, and to add a 

 good deal to our knowledge of the more intimate details of 

 its structure. 



I have thought it best to give a connected account of the 

 structure of the skull, instead of merely pointing out the new 

 features recognizable in it, because Prof. Seeley^s descriptions, 

 although, so far as I have personally compared them with 

 liis material, perfectly accurate, are very difficult to follow 

 without the actual specimens or casts of them at hand. 



Descrijjtion of the Skull R. 3587. 



The skull agrees exactly in general characters with that of 

 Gomphognathus, and I refer it to Diadtmodon hrowni, Seeley. 

 I can see no reasons for generically separating Gompho- 

 gnathus from Diademodon. The sliull lacks the anterior end, 

 probably some 3 or 4 centimetres being missing. 



General account of the build of the Skull. 



Viewed from above the skull is triangular in shape, the 

 widest part being at the extreme back across the squamosals. 

 The orbit is of medium size, placed about the middle of the 

 length of the skull, and facing outwards and partly upwards 

 and forwards. T)ie postorbital bar is robust and nearly 

 horizontal in position, and the frontal width is only about 

 ^ of the entire width of the skull in the middle. 



The temporal fossa? are large and are separated by the 

 very high and narrow sagittal crest. Posteriorly this crest 

 divides into two branches, Avhich sprtad outwards and pass 

 backwards at an angle of about 90° with one another. These 

 ridges rapidly drop towards the lower side of the skull as 

 they pass outwards, and form the inner sides of a pair of 

 shallow but well-marked grooves, placed almost vertically on 

 the back of the skull The outer sides of these grooves are 

 formed by the zygomatic arches, which rise pari passu with 

 the occipital crest as they are traced forwards. 



