CHELONIA. 75 



from the decomposition of the pyrites with which it is extensively permeated, that 

 the description must necessarily be confined to little more than general contour. 



The osseous case is somewhat less deep, in proportion to its probable length and 

 breadth, than in E. bicarinata, as will be seen by a comparison of their dimensions ; 

 it is consequently less sloped at the sides, which are also less curved. There is not 

 the slightest indication of a carina, either median or lateral ; but the whole vertebral 

 region is simply flattened. 



I have already had occasion to observe, that as the scutate Chelonians continue' to 

 grow, the vertebral scutes are observed to alter their form, and the relative proportion 

 of their longitudinal and transverse diameters. This takes place particularly by the 

 comparative abbreviation of the angular lateral projections which meet the line 

 of junction of the margins of the corresponding costal scutes. These angles, as the 

 animal grows, and as the scutes increase in size, become comparatively much shorter 

 and more obtuse ; and to such an extent does this take place, that in many species the 

 sides of the vertebral scutes become very nearly parallel in old age ; as may be 

 observed in the figure of E. bicarinata (T. XXV), and in most recent species. 



Now the specimen at present under notice, notwithstanding its great size, exhibits 

 this indication of old age, even in a less degree than in the figured specimen of 

 E. bicarinata. We could not, therefore, even if other distinctive characters were 

 absent, for a moment confound them as one species. 



In longitudinal dimensions the scutes in question ordinarily increase in proportion 

 to the growth of the animal ; and afford, in the examination of mutilated fossil Chelonian 

 remains, approximating data for ascertaining the general size of the animal ; the 

 second and third vertebral scutes, taken together, being generally rather less than 

 two fifths of the total length of the carapace. 



The edge of the present specimen, and the injuries it has undergone, combine to 

 render any satisfactory account of the vertebral series of osseous plates impossible ; the 

 nuchal and pygal plates being absent, and the neural wholly indistinguishable ; and the 

 plastron has been even more mutilated than the carapace. 



The impressions of the vertebral scutes are tolerably perfect, as far as regards the 

 second {v2), third {vz), and fourth {va). The second and tliird are about as broad as they 

 are long, irregularly hexagonal, and the lateral angles are but moderately produced ; 

 the third has the posterior margin shorter than the anterior ; the fourth is rather 

 longer than it is broad, and notably narrowed posteriorly. 



The plastron exhibits at least the usual expanse of form which belongs to the 

 typical Emydes, but its condition is such as to preclude any detailed description. 



Feet. Inches. Lines. 

 Probable length of the carapace ..... 1 9 



Probable breadth of ditto 1 5 



Depth 4 8 



