M. Dollo — Belgian Fossil Reptiles. 393 



the disappearance of the scutes has taken place by a progressive 

 diminution of their rigidity, a diminution in consequence of which 

 the skin has been gradually moulded upon the subjacent bone, 

 taking exactly its reliefs and hollows. At this stage it must have 

 already possessed a vermiculated external surface of the carapace (as 

 happens with the ThecopJiora, which have a soft skin, Trionyx for 

 example), but the dorsal tegument was always divided into distinct 

 areas, leaving their trace upon the above-mentioned external face. 

 Such is perhaps Anostira,^ and probably Chelonia Suyckerhuyhi. 

 Afterwards, these different areas have disappeared, and with them 

 their lines of demarcation on the skeleton : take Trionyx and 

 Pseudotrionyx as examples. We may then find, by future researches, 

 all the passages between the gymnoderm and lepidoderm ThecopJiora, 

 and I do not understand, consequently, how the presence or the 

 absence of horny scutes could suffice alone to characterize a family. 



11. Pachyrhynchus.^ — 1. As Messrs. Boulenger and Lydekker 

 have pointed out,^ this name has already been employed ; it 

 will therefore be necessary to change it. In a paper at present in 

 the press ^ I have proposed to substitute for it Erqiielinnesia, to 

 recall the locality in which the curious Chelonian has been dis- 

 covered, and where it is so common.^ 



2. As Messrs. Boulenger and Lydekker admit,^ and contrary ' 

 to the statement of Mr. E. D. Cope,'' my FacliyrhyncliincB^ are 

 quite distinct from the Fropleuridce^ of the celebrated Professor of 

 Philadelphia, since the latter have nine pairs of costal plates, 

 whereas the Chelonian of Erquelinnes has only eight, 



3. Mr. Cope, notwithstanding the assertion to the contrary of 

 Messrs. Boulenger and Lydekker,^" does not refer, at least in the 

 paper mentioned by them,^^ any of the species of Sir E. Owen 

 to Puppigerus}'^ Besides, as I have said in a former paper,^^ 

 Erquelinnesia is, without any doubt, generically different from the 

 American type, since the latter has the xiphiplastrons united by 



1 J. Leidy, ' Contributions to the extinct Vertebrate Fauna of the Western 

 Territories,' Rep. U. S. Geol. Surv. Territories (F. V. Hayden), Washington, 1873, 

 p. 174 and 175, pi. xvi. fig. 1 and 2. E. D. Cope, ' The Vertebrata of the 

 Tertiary Formations of the West' (book i.), Eep. U. S. Geol. Surv. Territories (F. 

 V. Hayden), Washington, 1883, p. 112. L. Dollo, 'Cheloiiiens du Bruxellien,' etc. 

 p. 95. 



2 L. Dollo, ' Premiere Note sur les Cheloniens landeniens (Eocene inferieur) de 

 la Belgique,' Bull. Mus. Roy. Ilist. Nat. Belg. 1886, t. iv. p. ^129. 



^ R. Lydekker and G. A. Boulenger, 'Chelonia,' etc., p. 270. 



* L. Dollo, ' Cheloniens oligocenes et neogenes,' etc. (v. supra). 



s L. Dollo, 'Cheloniens landeniens,' etc., p. 129. 



^ R. Lydekker and G. A. Bouleger, ' Chelonia,' etc., p. 271. 



' E. D. Cope, 'Dollo on Extinct Tortoises,' American Naturalist, November, 

 1886, p. 968. 



^ L. Dollo, Cheloniens landeniens,' etc., p. 139. 



^ E. D. Cope, ' Tertiary Vertebrata,' etc., p. 111. 

 1" R. Lydekker and G. A. Boulenger, 'Chelonia,' etc., p. 271. 

 ^1 E. D. Cope, ' Dollo on Extinct Tortoises ' (v. stt 

 '2 E. D. Cope, ' Tertiary Vertebrata,' etc., p. 112. 

 ^^ L. Dollo, ' Cheloniens landeniens,' etc., p. 131. 



