of the upper canines. The twelfth tooth, counting backwards, assumes the lamellate triangular shape of striate crown characteristic of the superior sectorials; and the inferior ones were lodged, like those above, in a common depression of an outer alveolar wall, developing the ridges dividing such depression into the dental recesses, as shown in fig. 7.
This approximation to a lacertian dental character might seem ground for something more than a family section of the Order Crocodilia. But the quasi-pleurodont attachment of the hinder teeth in Theriosuchus is only an extension of the character affecting some of those teeth in existing species of Crocodile[1], and successional teeth, or their indications, are in crocodilian relation with the roots of the teeth to be displaced.
In the cranial platform of Theriosuchus, fig. 1, the median parietal part of the hind border is less convex, and the two outer parts are more concave, by reason of the further backward production of the mastoids (12), than in the contemporary dwarf Crocodile which I have called Nannosuchus. The lateral borders of the sculptured part of the platform are more convex than in Goniopholis or Petrosuchus. This is owing to the greater proportion of the outer and posterior angles of the platform, which is abruptly depressed below the level of the sculptured surface of the mastoid, and which becomes smooth like the contiguous and lower-placed tympanic. This character, shown in the subject of fig. 1, Plate IX., usefully indicated fragmentary parts of the skull of other individuals of the species. The supratemporal vacuities (T) are relatively larger than in Goniopholis. The intervening tract of the parietal (7), more canaliculate than in the larger species, is divided by a mid ridge in two of the cranial specimens, and partially so in the more complete skull, fig. 1. No palpebral ossicle is preserved in the orbit, o; the pointed ends of the nasals are produced so as to divide the outer nostril into two (fig. 1, n, n), as in some specimens of Crocodilus niger; were this a character of generic value it might unite Theriosuchus with Halcrosia, Gray[2].
The alveolar part of the maxillary in which the canines are developed makes a corresponding convex extension of its outer border, as in Goniopholis. The extent of the 'symphysis mandibulæ' and the angle of divarication of the same are shown in fig. 2.
The matrix being removed from the palatal surface of the skull, fig. 2, exposed the orifice of the Eustachian canal, e, the palato-naris, pn, the pterygoids, 24, the palatines, 20, portions of the palatal plates of the maxillary, 21, and the pterygo-maxillary vacuities, y. The vertebræ, fig. 12, of Theriosuchus are amphiplatyan. The humerus, fig. 8, and the femur, fig. 9, have the Crocodilian structure.
- ↑ I have noted it in the Alligator niger. "No. 765. The right ramus of the lower jaw, from which the posterior part of the inner alveolar wall has been removed, showing the five posterior teeth lodged in a common alveolar groove." Osteological Catalogue, Museum of the Royal College of Surgeons, 4to, vol. i. p. 167 (1853).
- ↑ Trans. Zool. Soc. vol. vi. p. 135.
