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Show 1873.] DR. J. E. GRAY ON THE TRIONYCHIDcE. 45 2. NlLSSONIA. Skull elongate, tapering on the sides in front, the forehead suddenly bent down; the nose of the skull between the orbit and the oblong four-sided erect nose-hole notmore than half the diameter of the orbits. The front of the palate concave, with a narrow deep groove to the septum, between the internal nostrils, which is rather wider in front, and then about the same width behind, where it is very deep ; alveolar surface very wide, gradually tapering off towards the front of the mouth ; lower jaw very strong ; alveolar surface much wider in front than at the sides, with a deep, short, longitudinal pit in the front half of the front edge, which is rather concave. Hinder part narrower, concave, with a strong prominence on the inner edge. Nilssonia, Gray, Ann. & Mag. N . Hist. 1872, x. p. 332. The skull from which this genus is described was received in 1865, probably from India ; but I have not been able to find any Indian Mud-tortoise with which it could be identified. The skull is three inches long from the end of the nose to the posterior condyle, and an inch longer to the end of the central longitudinal ridge, and is two inches wide just in front of the tympanic aperture, which is the widest part of the skull. 1. NILSSONIA FORMOSA. (Fig. 2, p. 46.) Only young animal known. Back olive, with four large spots, with a black eye and a narrow white edge. Head with a spot behind each eye and at the angle of the mouth, and a large white transverse band on each side of the back of the head, interrupted in the middle of the upper part. Skull shorter and broader than that of the adult. Trionyx formosus, Gray, P.Z.S. 1869, p. 217, t. 15. fig. 1 (young); Suppl. Cat. Sh. Rept. p. 99. Hab. India (Pegu, Theobald's coll.). B. M . It appears that this and the other Trionyx marked " Pegu" do not really come from that place ; for although the collection was sold as from " Pegu," it contained many specimens from other parts of Hindostan. The skull of the very young animal described as Trionyx formosus (only -f inch long) in the British Museum, which has as yet no dorsal or ventral callosities, is very like the adult skull above described, but is shorter and broader, and the groove in front of the internal nostrils is deeper. I think that this is probably the effect of age, and that the skull becomes longer by growth. I have named this genus after m y old friend Dr. Sven Nilsson, of Lund, who has been working on zoology since 1816, and more lately on archaeology, and is now, in his 86th year, in the full vigour of his intellect. Two young specimens in spirits have no sternal callosities ; but all the bones of the sternum are seen through the skin. The back of the young is marbled, and has the four eyed spots like the young of the genus Trionyx. |