FLYING DRAGONS. 
4i 
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 flve-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 (J 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 not fail to notice an exact parallelism between ordinary bats and the more 
highly-developed fruit-bats. 
