CONCLUDING REMARKS. 273 



But this aspect of Reptilian life rapidly fades away as we pursue our course 

 through the dark vistas of the past. The slow and massive Chdonia, indeed, 

 characterised by their tenacity of life and the sluggishness of its manifestations, 

 continue to retain the characteristic forms of the principal modifications of their 

 Order, but little altered. The Chelone Camperi and Chelone Benstedi do not differ more 

 from the modern Turtle of gastronomic repute than do the numerous forms that 

 paddled about the estuary of Sheppey in the oldest Tertiary times. The modifications 

 of the Emydian from the Green-sand of Maidstone are not of greater value than may 

 be expressed by a sub-generic name, in accordance with the adopted practice of 

 modern Herpetologists. 



When, however, we look for species of the modern Crocodiles, Alligators, and 

 Gavials, in the strata that immediately follow the Tertiary beds in descending order, 

 we nowhere find an unequivocal trace of them. Not a fragment of the numerous 

 vertebrae that enter into the composition of the much- prolonged spinal column of the 

 procselian Crocodilia has yet been discovered in any of the widely-dispersed Formations 

 of the Chalk or Green-sand periods, although some of the latter were so situated as 

 to have received occasional evidences, as in the case of the Protemys, of the 

 Reptilian inhabitants of the Fresh-waters or Estuaries. 



The only Saurian vertebree with a cup at the front and a ball at the back part of 

 the body, from the Cretaceous deposits, belong to the Lacertian not to the Crocodilian 

 Order ; and the most remarkable of these vertebrae show a modification of the 

 Lacertian type very distinct from any existing form, being adapted more expressly for 

 aquatic, and without doubt marine, life, and, attaining, under favour of that medium of 

 existence, a bulk surpassing the largest of the modern Crocodilia. The Mosasaurus 

 combined a carnivorous form of teeth with an anchylosed mode of their attachment, as 

 in many Fishes and in the Acrodont Chameleons and Agamian Lizards, and with a 

 disposition of the teeth on the maxillary and pterygoid bones, as in many of the true 

 Lizards, and in the Anolian, Scincoid, and Iguanian famihes. The vertebral column 

 was modified for the act of swimming, by being unfettered by zygapophysial joints 

 along more than the hinder half of its extent, as it is in the Cetacea ; and by the 

 anchylosis of long haemal arches to the vertically-extended caudal vertebrae, as we find 

 in many Fishes : and the trunk, composed of one hundred and thirty-three vertebrae, 

 which supported a skull of four feet in length, cannot be reasonably calculated at less 

 than from twenty to thirty feet in length. The extremities, though doubtless webbed 

 and adapted for swimming, like those of the Gavial, yet appear, from the evidence 

 adduced in the text, to have been formed, as in the Crocodilian type, for occasional 

 locomotion on land ; yet the absence of any trace of a sacrum combines with the 

 ascertained modifications of the vertebral column, in indicating a more strictly marine 

 life in the Mosasaurus than in any modern Lizard. The ascertained modifications in 

 the structure of the skeleton of this large extinct Lacertian demonstrate, in fact, that 



