CATALOGUE OF SHIELD REPTILES. 



on the other hand, I found what I regard as skulls of the 

 same species inserted under three different names. 



The skull of a Crocodile which is found in the internal 

 rivers of India is named Crocodilus rhombifer, Cuvier, 

 (which is an American species,) though the specimen in the 

 College Museum was received from Bengal. 



I do not by any means regard my determination of these 

 skulls as infallible ; but I have taken every care to render 

 it correct by repeated examination. I first arranged the 

 skulls as they appeared to be alike, according to the cha- 

 racters here assigned to them, without paying any attention 

 to the names given, placing them in order according as 

 their size showed the change iu the growth; and Mr. Flower, 

 Mr. Gerrard, and some other zoologists who are used to the 

 examination of bones agree with me in my determination, 

 and were much interested in observing how gradually the 

 skulls of different ages glided into each other. 



I must observe, if there is this difference of opinion in 

 the determination of skulls of recent Crocodiles, where the 

 series of skulls of animals different in age can be compared, 

 and where the skulls are in a perfect state, how much 

 more difficult it must be to have confidence in the determi- 

 nation of the skulls of fossil species, where the skulls are 

 generally more or less imperfect, and perhaps only single 

 specimens (often very imperfect specimens) have been 

 examined ! 



The chief difficulty in distinguishing the species has 

 originated from the very great changes that take 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 differ- 

 ence may be divided into three stages, exemplified in the 

 young, the nearly full-grown, and the adult or aged speci- 

 mens. The head and beak of the young are generally de- 

 pressed, 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, swollen, and heavy, and 

 assumes a very different external form. 



It is to be observed that in all these changes in the ex- 

 ternal form of the skull, 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 for separating 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 obser- 

 vation 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 Cro- 

 codiles so difficidt. If this is the case with the recent 

 species, how much more caution is requisite to determine 

 the fossil remains of the animal ! Cuvier 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 pala;ontologists, 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 a genus 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 skull of each of the specimens 

 of the different species in the British-Museum collection ; 

 but I am satisfied that the importance of such tables of 

 measurements is overestimated : no doubt it has a very 

 imposing appearance ; but a good figure is more useful than 

 any amount of measurement. Every species has its normal 

 measurements ; but these are liable to vary in the different 

 individuals ; anil any difference sufficient to show a di- 

 stinction of species is easily appreciated by the eye, as it 

 must alter the general proportions of the different parts of 

 the head. 



It has been suggested that I ought to give the description 

 of each separate bone of which the skull is composed. This 

 may be of use to the student of comparative anatomy, but 

 is not of so much importance to the zoologist; for though 

 each bone has a normal form in each species of Crocodile, 

 yet they are each liable to considerable variation within 

 certain limits in the different individuals of the species. 

 The bones of the different genera have been described in 

 several works on osteology, and have been well figured by 

 De Blainville and others. 



De Blainville, in his ' Oste'ographie,' devotes five folio 

 plates to the osteology and dentition of recent Crocodiles, 

 giving details of Crocodilus biporcatus, C. lucius, C. vul- 

 garis, C. Schlegelii, C. longirostris, (J. rhombifer, and G. 

 sclerops. These plates were prepared to accompany an 

 essay that M. de Blainville was preparing for the ' Memoires 

 de l'Academie des Sciences de France ' when he died. 



Professor Carl Bernhard Bruhl, of the Universities of 

 Cracow and Pesth, has published twenty quarto etchings of 



b2 



