INTEODUCTION. xi 



while Abel, Auer, and Arthaber discussed more or less imperfect skeletons of 

 Metriorhynclius, sometimes incorrectly restored, from the Oxford Clay of Peter- 

 borough. 



A beautiful skeleton of a young individual of Geosaurus gracilis from the 

 Kimmeridgian Lithographic Limestone of Eicbstatt has lately been acquired by 

 the British Museum. This specimen, which has been described by Dr. L. v. Ammon *, 

 is figured in the Frontispiece and gives a good idea of the general appearance of these 

 sea-crocodiles. It is especially remarkable, because, to some extent, it shows the 

 outline of the body, and the form of the caudal fin (text-fig. A, p. xii) is beautifully 

 shown. Dr. Ammon believes that portions of the muscles are preserved in phosphate, 

 but it seems possible that these are fragments of wrinkled skin. The skull, which 

 in the original block was thrust back over the cervical vertebra? and tilted up, has 

 been freed from the matrix and placed in its natural position. 



The skeleton lies in a curved position on the left side, the dorsal surface being 

 turned to the concave side of the curve : one result of this is that the downwardly 

 flexed part of the tail is partly straightened out, so that the exact form of the caudal 

 fin is somewhat distorted. The total length of the skeleton along the curve is about 

 114 cm. (3 ft. 8\ in.), of which the skull occupies about 21 cm., the tail 51 cm. 



The skull and mandible are in close contact in their natural position. The 

 former is in the shape of an elongated triangle, the base of which is between a 

 quarter and a fifth of its height (?'. e., length of skull to tip of snout). The skull- 

 roof in the neighbourhood of the orbits is incomplete and consequently does not 

 show the form characteristic of the group, the overhanging prefrontals being lost. 

 The occipital and the antorbital regions of the skull are fairly well preserved. The 

 palatal region is much crushed and its structure obscure. The snout is relatively 

 longer and more slender than in any species of Metriorhynclius and none of the bones 

 preserved show more than a trace of sculpture. The form of the supratemporal 

 fossae is doubtful, the openings, as shown in the figure, being probably too small. 

 The external narial opening is elongated and without a median division. The teeth 

 are small and numerous, but their exact form and number cannot be determined. 



The anterior cervical vertebrae are incomplete, only three at the posterior end being 

 preserved, though much crushed. Behind the last, the slab has been broken across 



* " Uebgr jurassische Krokodile aus Bayern," Geognostische Jahreshefte, Jahrg. xviii. (1905) p. 62. 



52 



