288 Prof. H. G. Seeley. Researches on the Structure, [June 21, 



XV. " Researches on the Structure, Organisation, and Classifi- 

 cation of the Fossil Reptilia. Part IX. Section 4. On 

 the Gomphodontia." By H. G. SEELEY, F.R.S. Received 

 June 21, 1894. 



(Abstract.) 



The Gomphodontia is a group of Anomodont reptiles characterised 

 by theriodont dentition, in which the molar teeth are expanded trans- 

 versely, more or less tuberculate, and have the crowns worn down 

 with use, as in ungulate and other mammals. The orbit of the eye 

 is distinct from the zygomatic vacuity, which is conditioned as in the 

 Cynodontia, there being a long narrow parietal crest dividing the 

 temporal vacuities. There are two well-defined occipital condyles 

 united at the base, in a way that is closely paralleled in some 

 mammals. The occipital plate is triangular, as in mammals, with no 

 perforation except the foramen magnum. A deep superior notch 

 defines the occipital plate from the lateral external squamosal bar. 

 The malar bone, which forms the larger part of the zygoma, behind 

 the orbit, has a slight descending process which varies in develop- 

 ment. The hard palate terminates transversely in the middle length 

 of the molar teeth. There is a descending transverse palatine arch 

 situate behind the orbits. The incisor teeth are small and pointed ; 

 the canine teeth may be inconspicuous, but are usually large, com- 

 pressed, and serrated ; the premolars are small, circular, and usually 

 tuberculate ; the molars are usually single-rooted, in close-set series 

 which diverge as they extend backward, with crowns which vary in 

 form, but are commonly wider than long, and usually have the 

 external and internal cusps more prominent than the other tubercles 

 on the crown. 



The group is based chiefly upon the genera Gomphognathus, known 

 from skulls, a vertebra, and fragments of limb bones ; Trirachodon, 

 known from skulls only ; and Microgomphodon, in which the canine 

 teeth are no larger than the incisors. The last genus appears to 

 make known the more important parts of the skeleton. 



These specimens, collected by the author at Lady Frere, by Dr. 

 Kannemeyer, near Burghersdorp, and by Mr. Alfred Brown, near 

 Aliwal North, are all from the Upper Karroo rocks, on or about the 

 horizon of the Coal Beds. 



Of Gomphognathus there is a complete skull, with the lower jaw 

 attached, about 9 ins. long, a second skull which displays the palate, 

 and a separate lower jaw in connexion with part of the back of the 

 skull. These specimens show four incisor teeth in each premaxillary 

 bone, with sharp lateral serrated borders. The mandibular canine 

 is covered when the jaws are closed. The maxillary canine is a 



