MONOGRAPH 



ON THE 



FOSSIL REPTILIA OF THE LONDON CLAY. 



Supplement to the Order — CHELONIA. 

 Family — Paludinosa. 



Platemys Bowerbankii (?). Tab. XXIX, figs. 1, 2. 



The evidence of species of Chelonia of the Fresh-water or Marsh-dwelling family, 

 Paludinosa, has hitherto been derived only from such parts of the skeleton of the 

 trunk as have been described, figured, and referred to the genera Platemys and Emys, 

 in Part I of the present Monograph, pp. 62-76. 



Since those pages were sent to press, Mr. Bowerbank has been so fortunate as to 

 obtain from the Eocene clay at Sheppy the portion of fossil skull, of which two views 

 are given of the natural size in T. XXIX, figs. 1, 2. If these figures, and especially 

 the side view, fig. I, be compared with the corresponding view of the skulls, T. I, 

 fig. 1 ; T. Ill, fig. 1 ; T. XV, fig. 1, or T. XI, fig. 2, a marked difference will be dis- 

 cerned in the form and proportion of the orbit, which is smaller and more nearly 

 circular in fig. 1, T. XXIX. 



But the bony chamber for the eyeball forms one of the characters by which the 

 skull is distinguished in the marine and fresh-water families of the order Chelonia. 

 The orbit, for example, is always much larger in proportion to the entire skull in the 

 marine species, and commonly of the oval form, which is preserved in the beautiful 

 fossil skull of the Chelone cuneiceps, T. XV, fig. 1 ; or with the upper and outer part 

 even more produced and angular than is there represented. In the families Fluvialia 

 (Trionyx) and Paludinosa (Emydians), the orbit is not merely much smaller in propor- 

 tion to the skull, it is circular, or nearly so, and not produced at the upper and outer 

 angle. By this character, we are led to refer the fossil skull under description to 

 the fresh-water division of the Chelonian order. 



Our choice between the Fluviatile or Paludinose families of that division is guided 

 by the formation of the border of the orbit, and by the proportionate length and the 

 form of the face or muzzle in advance of it. 



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