FLYING DRAGONS. 41 



Chalk was deposited. They are represented by several well-marked types, which 

 may be arranged under three family groups. Of these the most specialised forms 

 are the toothless pterodactyles, or pteranodonts, from the Cretaceous rocks of North 

 America ; some of these toothless members of the order far exceeded any flying 

 bird in point of size ; the estimated span of wing in the largest species being 

 upwards of five-and-twenty feet. This group may be distinguished not only by the 

 total absence of teeth, but likewise by the great backward extension of the hinder 

 extremity of the skull. 



In the typical pterodactyles (Pterodactylus. etc.) the jaws were provided with 



restoration op a long-tailed pterodactyle {\ nat. size). — After Marsh. 



teeth, — which may, however, have been very small in size and few in number, — 

 while the skull, as shown in the figure of the skeleton on p. 40, was not produced 

 backwardly, and the tail was reduced to a rudiment. The members of this group, 

 which are common in the Oolitic rocks of the Continent, vary in size from the 

 dimensions of a sparrow to those of an eagle. Lastly, we have the long -tailed 

 pterodactyles (Rhamphorhynchus, etc.), which are likewise of Oolitic and Liassic 

 age, and are at once distinguished, as shown in the restoration, from the members 

 of the preceding group by the fully developed tail. These long-tailed species are 

 evidently the most generalised members of the order ; and in the retention of the 

 tail in the generalised group, and its loss in the more specialised one, the reader 

 will hot fail to notice an exact parallelism between ordinary bats and the more 

 highly-developed fruit-bats. 



