30 



distinct genera, the name Pterodactylus should be retained for the 

 longirostral species, as including the first-discovered specimen and 

 type of the genus ; and the crassirostral species should be grouped 

 together under some other generic name. 



The specimen of gigantic Pterodactyle described by Mr. Bower- 

 bank at the last meeting of the Society consists of the solid anterior 

 end, i. e. of the imperforate continuous bony walls, of a jaw, com- 

 pressed and decreasing in depth, at first rapidly, then more gradually, 

 to an obtusely-pointed extremity. As the symphysis of the lower 

 jaw is long and the original joint obliterated, and its depth somewhat 

 rapidly increases by the development of its lower and back part into 

 a kind of ridge in some smaller Pterodactyles, the present specimen, 

 so far as these characters go, might be referred to the lower jaw, and 

 its relatively inferior depth to the upper jaw in the Pt. conirostris 

 would seem to lead to that conclusion. But the present is plainly a 

 species which has a longer and more slender snout in proportion to its 

 size, and the convex curve formed by the alveolar border, slight as it 

 is, decides it to be part of the upper jaw. The lower jaw, moreover, 

 might be expected, by the analogy of the smaller Pterodactyles, to be 

 flatter or less acute below the end of the symphysis. 



The specimen of Pt. Cuvieri consists of the anterior extremity of 

 the upper jaw, of seven inches in extent, without any trace of the 

 nasal or any other natural perforation of its upper or lateral parietes, 

 and corresponds with the parts marked a, b, in figs. 10 & 1 1. From 

 the number of teeth contained in this part, the Pt. Cuvieri presents 

 a much closer resemblance to the Pt. longirostris than to the Pt. 

 crassirostris ; and if the entire skull were restored according to the 

 proportions of the Pt. longirostris, it would be twenty-eight inches 

 in length. 



But nature seems never to retain the same proportions in species 

 that differ materially in bulk. The great Diprotodon, with the den- 

 tal and cranial characters of a Kangaroo, does not retain the same 

 length of hinder limbs as its living homologue ; the laws of gravity 

 forbid the saltatory mode of locomotion to a Herbivore of the bulk of 

 a Rhinoceros ; and accordingly, whilst the hind-legs are shortened 

 the fore-limbs are lengthened, and both are made more robust m the 

 Diprotodon than in the Kangaroo. The change of proportions of 

 the limbs of the Sloths is equally striking in those extinct species 

 which were too bulky to climb, e. g. the Megatherium and Mylodon. 

 We may therefore infer, with a high degree of probability, when a 

 longirostral Pterodactyle much surpassed in bulk the species so called 

 ' par excellence,' that the same proportions were not maintained in 

 the length of the jaws ; and that the species to which the fine frag- 

 ment belonged, far as it has exceeded our previous ideas of the bulk 

 of a flying reptile, did not sustain and carry through the air a head of 

 two feet four inches in length, or nearly double the size of that of the 

 Pelican. 



Although the fractured hinder part of the jaw of the Pt. Cuvieri 

 shows no trace of the commencement of the wide nasal aperture, there 

 is a plain indication that the jaws were less prolonged than in the Pt. 



