Prof. Owen on the genus Dicynodon. 71 



complementary piece, instead of the insignificant size to which it is reduced in 

 the Crocodiles and most Chelonians, presents proportions surpassing those of 

 most Lacertians ; the upper margin for the attachment of the temporal muscle 

 is intermediate in height between that in the Crocodiles and the more angular 

 elevation of the coronoid in most Lizards. In the proportion of the dentary to 

 the other elements of the composite bone, the Dicynodon resembles the Lacer- 

 tians, the dentary piece forming a much larger proportion of the lower jaw in the 

 Crocodiles and Chelonians ; but the entire structure of the bone exemplifies, as 

 remarkably as the rest of the skull, the singular engrafting of Crocodilian and Che- 

 Ionian characters upon an essentially Lacertian basis. 



Dicynodon testudiceps. 



The specimen on which the above-named, or tortoise-headed, species of Dicy- 

 nodon is founded is the anterior two-thirds of a skull, without lower jaw ; including 

 the nostrils, the orbits and the bony palate, with the anterior and posterior palatal 

 apertures (PI. V. & PI. VL fig. 1.). 



It differs in a readily appreciable and well-marked degree from the last-described 

 skull of the Dicynodon lacerticeps, by the greater breadth and less length of the 

 facial part of the skull, by the smaller orbits and larger nostrils, and by the greater 

 declivity of the contour of the internasal and intermaxillary regions. In D. lacerticeps 

 (PI. III. fig. 1.) the profile of the internasal plate is continued from the inter-orbital 

 region, with a slight declivity, almost straight to the intermaxillary bone. In D. 

 testudiceps (Vl.YI. fig. 1.) the profile bends down directly from the inter-orbital region, 

 and rapidly descends to the edentulous border of the intermaxillary bone. The 

 distance from the posterior border of the orbit to the anterior border of the nostril is 

 rather less in the Dicynodon testudiceps than it is in D. lacert'ceps ; but the breadth 

 between the supra-orbitary ridges in Dicynodon testudiceps is greater, being one 

 inch and two-thirds, and that between the supra-nasal ridges is one inch. The 

 general size of the two fossil skulls compared must have been nearly alike : their 

 specific difference will be obvious from the comparisons above made : the generic 

 identity of the shorter and broader-headed species is shown by the bases of the two 

 large tusks which remain in the sockets of the expanded maxillaries, their exserted 

 crowns having been broken off (PI. V. fig. 1, c). 



The breadth and shortness of the skull, the sudden convex declivity of the rostral 

 part, and the sharp vertical, edentulous border of the wide intermaxillary bone, are 

 features of resemblance to the skull of the Tortoise which would at once strike the 

 anatomist acquainted with the peculiar form of that part of the skeleton of the 

 Chelonian Reptile ; and they have suggested to me the specific name proposed 

 for the present species. But diflferences of a more essential nature present them- 



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