128 DE. J. E. GRAY'S SYNOPSIS OF THE SPECIES 



The chief difficulty in distinguishing the species has originated from the very great 

 change of forms that takes place in the shape and proportions of the head of the animal 

 in its different stages of growth ; but the changes seem nearly similar in all the species, 

 and therefore when once observed they can be easily allowed for. The difference may 

 be divided into three stages, exemplified in the young, the nearly full-grown, and the 

 adult or aged specimens. The, head and beak of the young are generally depressed, with 

 more or less distinctly marked symmetrical ridge and depressions ; and these characters 

 are gradually modified until the animal assumes its nearly full size, — the skull becoming 

 thicker and more solid, but yet retaining most of the characters that distinguish its 

 young state. After this period, as the animal increases in age, the skull becomes more 

 and more convex and swollen and heavy, and assumes a very diflerent external form. 



It is to be observed that in all these changes in the external form of the skuU, the 

 bones themselves of which it is composed preserve their general form and relation to 

 each other ; and the sutures between these bones appear to me to offer some of the best 

 characters to separate the species into groups. In many instances, when I have been in 

 doubt, the sight of the intermaxillary suture has at once solved the difficulty, which has 

 been verified by the examination of the locality of the specimen. 



These changes in the form of the head have been among the causes that have made the 

 study of the species of Crocodiles so difiicult. If this is the case -v^dth the recent species, 

 how much more caution is requisite to determine the fossil remains of the animal ! 

 C'u^'ier set a very good example in that respect : he commenced the study of each group 

 of animals with an examination of the osteology and external characters of the living 

 species, and then applied the knowledge he thus acquired, to the distinction of the fossil 

 remains ; but now we often find palaeontologists, as they call themselves, neglecting, or, 

 at most, only taking the outline of the osteological and zoological characters of the living 

 species at second hand, and describing the fossil, and often forming genera and species 

 on a small fragment, thus encumbering the science with a multitude of names. 



At one time I proposed to give accurate measurements of the different parts of the 



713. Crocodihis acutus=Oo2}holis porosus of India. 

 715. Crocodihis acutiis= Crocodilus vulgaris of Africa. 



717. Crocodihis vulyaris, much distorted. 



718. Crocodihis vulgaris= Bomhifrons, perhaps B. siameiisis. 

 719-724, 727, 728. Crocodihis biporcatus= Oopholis porosiis. 



725. Crocodihis hijiorcatiis^ CrocodiJtis vulgaris. 



726. Crocodihis biporcatus^Bomhifrons indicus. 



750, 751. Crocodihis rhombifer, from Bengal^ Bombifrons indicus. 

 752. Crocodilits pahistris'7=Bombifrons indicus. 

 760-762. AlUgator hici us = Alligator mississippiensis. 

 764. Alligator niger=J<icure nigra. 

 ' Dr. J. E. Gray " On the Change of Form of the Heads of Crocodiles," Transactions of the Sections in ' Report 

 of the British Association of Science,' Cambridge, 1862, p. 109. 



