Genus 6. Rhynchosuchus.
There are twenty teeth above, and eighteen or nineteen below, on each side; the mandibular symphysis extends to the fifteenth tooth. The posterior teeth of the upper jaw, and almost all those of the lower jaw, are received into interdental pits; the orbital margins are not raised; and the premaxillæ are hardly at all expanded. The premaxillo-maxillary suture does not reach the third tooth behind the notch.
I propose the name Rhynchosuchus to indicate that generic type which is at present represented by the solitary species called by Müller and Schlegel Crocodilus (Gavialis) Schlegelii, and admirably described and figured by them in their essay, 'Over de Krokodilen van der Indischen Archipel,' in the 'Verhandelingen over de natuurlijke Gesch. der Nederl. overzee. Bezittingen,' 1839-1844. Under the title Crocodilus (Gavialis) Schlegelii (p. 18), they say—"The Gavial from Borneo, when compared with the Indian one, is principally distinguished by the following characters:—
"1. By its stronger form and better developed limbs.
2. By its much less slender head and snout, which last does not narrow so suddenly in front of the eyes as in G. Gangeticus.
3. By the smaller number of teeth, of which there are twenty above and eighteen below on each side, while G. Gangeticus has 28/26 or 27/25; furthermore, the teeth are stouter, less curved, and less sharp, and are disposed more perpendicularly, and the ninth tooth of the upper jaw (reckoning from the front) is considerably larger and stronger than the others; whence it follows that, just as in the true Crocodiles, the snout at the level of this tooth exhibits a lateral projection.
4. By the shorter symphysis of the under jaw.
5. By the absence of the swollen nasal prominence (neusklep), which characterizes the Gangetic Gavial.
6. By the less expanded form of the tabular upper surface of the hinder part of the skull.
7. By the very slight production of the edges of the orbit.
8. By the large eyes.
9. By the presence of a number of small nuchal shields, while G. Gangeticus has but one pair.
10. By the strongly developed keels of the dorsal scutes.
11. By the much larger scales on the under parts and on the legs of the animal.
12. By the different colours with which it is variegated."
These authors further point out that the vomers appear for a small space in the posterior part of the palate, that the opercular or splenial bones join in the symphysis of the lower jaw, and that the cervical and dorsal scutes form one continuous shield; and they represent the two anterior mandibular teeth passing in grooves on either side of the end of the premaxilla. In fact, they fully and completely establish the fact that their new species belongs to the Longirostres of Cuvier, or to the Gavials of later writers.
Under these circumstances, it is somewhat surprising to find the deliberate conclusions of these careful investigators set aside in the following brief passage:—
"This Bornean species (C. Schlegelii) was, in fact, originally described as a new species of Gavial; but the nasal bones, as in the fossil from Sheppey, figured in t. ii. 15, extend to the hinder border of the external nostril."—Owen, Fossil Reptilia of the London Clay, Crocodilia, p. 15: 1850.
Müller and Schlegel give remarkably clear and beautiful figures of the skull of their Gavial; and these show at once that the nasal bones do not "reach the hinder border of the external nostril," but meet the premaxillaries at a point very distant from that border, viz. opposite the ninth tooth. Even did the nasal bones reach the posterior boundary of the nostril, such a character would not outweigh those derived from the relations and number of the teeth, the structure and extent of the mandibular symphysis, and the disposition of the dermal scutes,—all of which are so clearly and definitely set forth by Müller and Schlegel, that it seems difficult to understand how any one who had consulted the original memoir could have overlooked them.
It was possible, however, that Müller and Schlegel, notwithstanding their great opportunities, might have erred in their statements; and I therefore gladly seized the opportunity of testing their description by comparing it with an authentic skull of the species in question, from New Guinea, in the collection of the British Museum.
I have found the statement of Müller and Schlegel minutely accurate in almost all points; and there cannot be the slightest doubt, not only that the Schlegelian crocodile is one of the Gavialidæ, but that it forms a distinct generic type in that family, as different from Gavialis as Caiman is from Jacare, or Mecistops from Crocodilus.
The following are the most important measurements of the skull of Rhynchosuchus Schlegelii in the British Museum collection:—
| Inches. | |
| Length from the end of the premaxilla to that of os quadratum | 23 |
| Breadth from outer edge of one os quadratum to that of the other | 83/4 |
| Breadth across the face in front of the orbits | 4 |
| " at the 9th tooth | 2 |
| " at the 5th tooth | 11/2 |
| " at the 3rd tooth | 13/4 |
| " of the beak-like curved process which carries the two anterior teeth | 1 |
| Mean width of lower jaw from symphysis to extremity | 15/8 |
| Length | 12 |
| No tooth measures transversely more than | 3/16 |
The face is very smooth; but a slight longitudinal groove runs down on each side from the anterior margin of the orbit for about two inches. Anteriorly to this point the snout retains a nearly even diameter as far as the ninth tooth, in front of which it suddenly narrows a little, retaining nearly the same dimensions to the fourth tooth, where it widens a very little, and then suddenly narrows to the terminal beak. The lower jaw does not expand at all at its extremity. The nasals join the premaxillaries opposite the ninth tooth, and the splenial bones, in the lower jaw, end opposite the tenth mandibular tooth, as the figures of Müller and Schlegel show. The vomers appear between the inner edges of the palatines posteriorly, as a thin bony band 13/8 inch long by 1/8 inch wide, which tapers at each end and is divided by a longitudinal suture. The ninth tooth of the upper jaw is stronger than the rest.
The only point in which the description of Müller and Schlegel seems to me to be incomplete[7] is with regard to the disposition of the teeth. They say—"The teeth of C. Schlegelii, as regards their form and development, more nearly resemble those of the true Crocodiles; but in the way in which the teeth of the two jaws are opposed, there is the most complete resemblance between our species and the Gangetic Gavial,—both which species differ from all other crocodiles in the circumstance that when the mouth is shut, all the teeth of the under jaw project outside the lateral margin of the upper jaw" (l. c. p. 22).
What I find is this:—The anterior teeth of both the upper jaw and the mandible are long, slender, sharp-edged, and slightly curved. The posterior eleven, on each side, in the upper jaw, are short, straight, conical, and constricted below their crowns. There are deep interdental pits between the ten posterior mandibular teeth, into which the opposed teeth of the maxilla are received when the jaws are closed. All the mandibular teeth, except the two anterior and the fourth pair, pass into like pits in the upper jaw. The anterior eight teeth on each side of the upper jaw pass straight down outside the lower jaw. In the Gangetic Gavial the relations of the teeth of the two jaws appear to me, as I shall state below, to be very different.
Rhynchosuchus Schlegelii inhabits the inland lakes of Borneo, and is found in New Guinea.