CATALOGUE OF SHIELD REPTILES. 



The head of the Crocodile first increases in length com- 

 pared with its width, and then, having arrived at a certain 

 form, increases in width, thickness, and solidity. 



The same change takes place in the head and skull of the 

 Bornean Garial, Tomistoma Sehlegelii, as is found in Miiller 

 and Schlegel's figures of the half-grown and adult skulls in 

 their work. 



It is to be observed that each of the Crocodiles of India and 

 Africa (and it may also be the case with those of America) 

 seems to present two varieties — one with a broad and the 

 other with a narrower face ; this variation occurring in each 

 of the species appears to me to show that it is more probably 

 a local, or perhaps even sexual variation than a specific 

 distinction. 



If it were a sexual distinction it might soon be settled 

 by observers in the country where they abound ; but the 

 sex of the skins and of the skulls sent to Europe is rarely, 

 if ever, marked on the specimens. 



The broad-nosed variety is much more abundant in the 

 Museum than the narrow-nosed one ; and this is against 

 the form of the face being a sexual distinction, as one 

 would suppose that they would be nearly equal in number, 

 unless the narrow-nosed specimens are the males and they 

 are more wary and not so frequently caught. 



Some naturalists might be inclined to regard them as 

 distinct species ; but in the Museum series, large as it is, 

 we have not sufficient materials to decide the question with 

 any confidence. Perhaps, if the skulls of specimens from 

 each locality could be compared, other characters might be 

 found; but this must be left for my successors in this field 

 of research. 



In the short-nosed species the upperside of the inter- 

 maxillary bones is short, and the nasal bones are produced 

 between their edges to the edge of the nostril ; and in the 

 genus Halcrosia they are produced beyond it, and form a 

 bony septum between the nostrils. In the long and slender- 

 nosed species the intermaxillary bones are rather produced 

 behind, and the nasal bones do not reach the edge as does 

 the long nostril in the genus Mecistops ; they are consider- 

 ably short of it ; but still the nasal bones come between 

 the hinder ends of the intermaxillaries, and this character 

 at once separates the skull of that genus from the two 

 genera of Garials which have short nasal bones. 

 The skulls of Crocodiles may be separated thus : — 



1. Nasal bone produced and separating the nostril into 

 two parts. Halcrosia. 



2. Nasal bone produced and dividing the edges of the 

 nostril. Oopholis, Crocodilus, Molinia (americmia), Bom- 

 bifrons, Palinia. 



3. Nasal bone not reaching the nostril. Molinia (inter- 

 media), Mecistops. 



The intermaxillary bone in Bombi/rons and Palinia is 

 short and truncated behind. In Halcrosia it is rather pro- 

 duced behind, the straight sides converging to a point. In 

 all the other genera it is produced behind, with the 

 hinder edges converging on the sides and truncated at tin 

 end. 



The palatal bone in all the genera is truncated or rounded 

 in front, except in Mecistops, where it is narrow, short, and 

 acute in front. 



The skulls of the genera Bombifrons, Oopholis, and Mo- 

 linia are easily distinguished in the young state, — the face 

 of Oopholis being much longer and narrower than that of 

 Bombifrons, and that of Molinia longer and narrower than 

 that of Oopholis. The following measurements are for 

 three skulls which appear to be from animals nearly of the 

 same state of growth, in inches and lines : — 



Bombifrons. Oopholis. Molinia. 

 in. Hues. in. lines, in. linee. 



Length of skull, entire 48 58 69 



Length of face to front of orbit 2 8 3 4 4 



Length of forehead to front of 



orbit 2 2 1 2 4 



Length of palatine from con- 

 dyle to front end 2 11 3 4 3 10 



Length of middle suture of 



maxilla 1 2 1 \\ 1 7 



Length of middle suture of in- 

 termaxillaries 9 1 3 1 6 



Width at occiput 2 6 2 5 2 10| 



Width at hinder contraction of 



beak 1 6 1 4 1 4i 



Width at notch 9 9 9 



The dorsal scales present considerable variations in dif- 

 ferent specimens from the same locality ; but, allowing for 

 such variations, the genera may be arranged thus : — 



1. The dorsal scales nearly uniformly keeled, in four or 

 six longitudinal series; the outer series ovate-elongate. 

 Oopholis, 



2. The dorsal scales nearly uniformly keeled, quadrila- 

 teral as broad as long. Crocodilus, Palinia, Molinia, and 

 Mecistops. 



3. The dorsal scales quadrilateral, as broad as long ; the 

 vertebral series scarcely keeled, the lateral series irregular 

 and keeled. Halcrosia and Molinia. 



The eyelid of the genus Halcrosia is thickened with hard 

 bony plates, as in some of the Alligators, with which it also 

 agrees in the external form of the head and the disposition 

 of the nuchal shield. In all the other genera it is thin and 

 membranaceous. 



