234 BRITISH FOSSIL REPTILES. 



In the Iclithyosaurus tenuirostris, the length of the lower jaw equals at least fourteen 

 times that of the vertical diameter of the centrum of an anterior caudal vertebra ; in 

 the Ich. communis and in the Ich. loncModon eleven times ; in the Ich. Iniermeduis ten 

 times the same diameter. The jaws of the Ichthyosaums camjjylodon must have 

 approached more nearly to the proportions of those of the Ich. tenuirostris, than the 

 other species above named, and it is not unlikely that the lower jaw was thirteen times 

 the length of the vertical diameter of an abdominal or anterior caudal centrum. 



Assuming such proportions, we may reckon the lower jaw to have been upwards 

 of four feet in length ; and this calculation accords with that founded upon the 

 proportions of the fragments of the lower jaws above described. 



One of the masses of chalk contains portions of several ribs, the longest being 

 about ten inches in length ; the transverse section of these portions of rib is a regular 

 full ellipse, the fractured end of one of the least mutilated is 9 lines in its long 

 diameter, 6 lines in its short diameter ; but some parts of the ribs are 1 inch in 

 breadth. Not any of these fragments show the opposite longitudinal impressions 

 that characterise some of the ribs in the Iclithyosaurus communis. 



CHAPTER V. 



Order. PTEBOSAUBIA, Owen. 



Genus — Pterodactylus, Cuvier. 



The honour of having first made known the existence of remains of Pferodactyles 

 in the Chalk belongs to the able Secretary of the ' Paleeontographical Society,' James 

 Scott Bowerbank, Esq., F.R.S. This indefatigable Collector had the good fortune 

 to receive, in 1845, from the Chalk of Kent, the characteristic jaws and teeth, with 

 part of the scapular arch and a few other bones of a well-marked species of Pterodactylus, 

 and the discovery was briefly recorded in the ' Proceedings of the Geological Society 

 of London' for May 14th, 1845,* with an illustrative plate. Mr. Bowerbank concludes 

 his Paper by referring to a large fossil wing-bone from the chalk, which I had previously 

 figured and described in the ' Geological Transactions,'! and remarks that " if it should 

 prove to belong to a Pterodactyle, the probable expansion of the wings would reach 

 to at least eight or nine feet. Under these circumstances," he says, " I propose that 



* The author there states that the specimens were " obtained from the Upper Chalk of Kent :" 

 Mr. Toulmin Smith, in his able paper " On the Formation of the Flints of the Upper Chalk" in the 

 •Annals of Natural History,' vol. xx, p. 295, affirms that no Upper Chalk exists in the localities whence 

 those specimens came. They are from the Middle Chalk. 



•\ Second Series, vol. vi, 1840, pi. 39, fig. 1. 



