TRIASSIC LA.BYRINTHODONS. 189 



the same remarkable fossil being given, reduced to one tliird the natural size, 

 in Plate XXXI, Vol. IV. 



By a comparison o£ these figures with those of the skulls of other extinct 

 species which have left their remains in the same formation and locality it will be 

 seen that besides difference of size, which is sufficiently remarkable, there are also 

 proportional characteristics which compel a reference of the giant of the marine 

 family to a distinct species. The entire skull is more flattened and depressed. 

 This is shown in figs. 1 and 3 of PI. XXXI. If they be compared with figs. 1 

 and 3, PL XI (Ghelone cuneicejys). Vol. II, which offers the nearest approach to Ch. 

 gigas in this character, the difference will be obvious. It is not wholly due to 

 posthumous pressure, although this has produced a partial dislocation, as shown 

 by the slightly bent super-occipital in fig. 3, and the shape of the orbit in fig. 1, 

 PI. XXXI. The plane of the nostril is wholly upon the upper surface of the 

 skull, and is relatively nearer to the orbits, and further from the anterior 

 premaxillary part. A transverse line across the back part of the nostril crosses 

 the orbit very little in advance of the hind part of the anterior third of that 

 cavity, a rare relative position of the nostril which could not have been induced by 

 mere pressure. The orbits open upon the anterior half of the skull. The 

 premaxillaries are produced beyond the nostril for a greater relative extent than in 

 any of the extinct kinds, in some of which, for example Ghelone longiceps (PL XII, 

 fig. 2), Vol. II, the plane of the aperture is the same with that of the fore slope 

 of the skull. In the recent Turtles, Ghelone mi/das, for example, the nostril is 

 terminal, and its plane almost vertical, and it opens wholly in advance of the orbits. 

 These apertures are relatively smaller in Ghelone gigas than in any recent and in 

 most extinct species. 



All the cranial characters of the marine family of the order Ghelonia are 

 present in the gigantic extinct species. 



Order— LABYRINTHODONTIA. 



Genus — Labyrinthodon, Oiven. 



A knowledge of the chief character of the present Oi'der and Genus was 

 derived from examination of portions of petrified teeth found in a quarry of the 

 New-red Sandstone at Coton End and Guy's Cliff, Warwickshire, and transmitted 

 to me for determination and description by Murchison and Strickland.^ The 

 specimens received indicated a tooth of the common canine character, but straight 



1 See their paper iu the ' Transactions of tlie Geological Society,' 4to, vol. v, Part ii, 1840. 



