398 AMERICAN TESTUDINATA. Part II. 



fossil remains of Caithness referred to this iamily are those of an extinct family 

 of Fishes.^ The oldest deposits in which true TrionychidiB have been observed 

 are the green sands of New Jersey, according to Dr. Leidy.^ Professor Owen 

 describes and illustrates very fully a number of tertiary species, which are the 

 oldest he has seen.^ 



I. Am YD A, Schiv. (Ag.) 



The head is long, low, narrow and pointed in front, and the angle of the 

 front part wdth the brain-box comparatively small. The nasal region is com- 

 pressed sidewise, and drawn out long and narrow. The nostrils are cut in a 

 peculiar way, and are not subdivided on each side by an internal ridge, as is 

 the case in Aspidonectes and Platypeltis (PI. 6, fig. 2a, 3a, 4a, and 7) ; they 

 lie rather under than at the tip of the proboscis, are widely apart, broader 

 below, and converge and taper upwards. The outer surface of the maxilla- 

 ries curve inward under the eyes and nose, so that the mouth is small and the 

 nasal region rounded. On account of the compression spoken of above, the 

 sides of the mouth are concave outward from the hind to the front end, and 

 that part of it which is under the nose is narrow and long. The alveolar edge 

 of the upper jaw is turned down farthest at the front end, and less and less 

 backward, fading out before reaching the hind end of the maxillaries ; it is sharp 

 in front, and toothed near the hind end ; but the teeth, though quite prominent 

 in the bill, are hardly perceptible in the jaw itself The horizontal alveolar sur- 

 fiice is narrow; it is widest near the hind end, curves down under the eye, and up 

 again under the nose. There is in this genus a large opening in the skull between 

 the maxillaries and the vomer. The lower jaw is also compressed sidewise and 

 drawn out long and narrow under the nose, and its sides are concave outward. 

 Its lower edges meet from the two sides where the compression begins, and the 

 narrowed part lies at the sides of the symphysis, and the latter is carried far 

 forward in rising from the lower to the upper edge of the jaw. The long, nar- 

 row alveolar surface thus formed at the symphysis descends inward from the outer 

 edge, slightly at the front end, more and more backward, and from the symphy- 

 sis to the angle of the jaw that surface is very narrow and almost vertical. 

 The alveolar edges are sharp all round. Thus we have in this genus a small 



' See Part II., Chap. 1, Sect. 17, p. 303. ' R. Owen and T. Bell, Fossil Eeptilia of the 



2 Troc. Ac. Nat. Sc. Phil. vol. 5, 1851, p. 329, London Clay, in Trans, of the Palajont. Society, 

 and vol. 8, 185G, p. 73. Londoji, 1849, p. 46. 



