n\ THE FAUXA AND FLORA OF TRR TRIAS OF THE RRITIf^H T8LES. -295 



therefore been made witli the aid of all the most important materials 

 hitherto discovered. 



Getiprnl Form. — As already remarked hy Huxley (4) the general 

 proportions of <lio head, trunk, and limbs of Iihynclin>tai(Tiiii arflcpps 

 closely resemble tliose of the existing Sphniodon jmnctafum, but the 

 extent of the long tail remains undiscovered. An outline-sketch of tlie 

 upper aspect of the skeleton, so far as known, is given in the accompanying 

 text-figure. 



iSkiiJl and 3fandihh\ — The skull is elongate-triangular in shape, with 

 a flattened roof which imparts to it a depressed appearance. Its external 

 surface is not ornamented, but many of the sutures between the constituent 

 brtnes are obscure or unrecognisable. Tlio oi'bits are large, occupying 

 the greater pai't of the middle third of the skull, and are directed both 

 outwards and upwards, with a conspicuously everted rim. The superior 

 and lateral temporal vacuities are also relatively large ; while the single 

 narial opening is quite small and terminal, situated between the upper 

 ends of the beak - like premaxillse. The occipital and basioccipital 

 regions of the cranium remain unknown ; but the bi-ain-case between the 

 temporal fossae is narrow, and the gently rounded parietal roof is sur- 

 ]nounted by a prominent median longitudinal crest, from the anterior end 

 of which a pair of less elevated though equally sharp ridges diverge 

 outwards along the frontal-postfrontal sutures to the upper m.argin of the 

 orbits. It is quite clear that there is no pineal foramen. The quadrate 

 bone, which is well exposed from behind in the type specimen (8. 1 '), is 

 deep and narrow, but not constricted above the trochlear lower end like 

 the corresponding bone (^f Sphenodoii. It is therefore probable that the 

 quadrate was dii'ectly in contact with the quadrato-jugal throughout its 

 depth, without any intervening postero-temporal foramen. The complete 

 lower temporal arcade, consisting of the jugal and quadrato-jugal, has not 

 hitherto been observed ; but the shape of the triradiate jugal, which 

 forms the orbital rim postero - inferiorly, shows that the arcade in 

 question must have been present. The lower edge of the jugal below the 

 orbit is everted, producing a short longitudinal ridge on the cheek. The 

 upper temporal arcade is formed chiefly by the large postorbital bone, 

 which is triangular in shape and only enters the hinder part of the 

 orbital rim for a short space between the jugal and postfrontal. Remains 

 of the squamosa], at the upper end of the quadrate in the tyjie specimen, 

 show that this element underlies the hinder end of the postorbital, and 

 extends in the usual inwai'dly directed jJrocess towards the parietal. As 

 displayed especially well in the type specimen, the roof of the facial 

 region of the skull is indented Avith small pits, which are more or less 

 irregularly disposed, but form a regular pair of lather deep depressions on 

 the nasal bones. The frontal elements constitute a diamond-shaped area 

 about as broad as long, and scarcely enter the orbital rim between the 

 relatively large postfrontals and prefrontals. The nasals, which form tlie 

 postero-superior boundary of the single narial opening, are excluded from 

 contact with the maxilla on each side by the long and downwardly curved, 

 spine-.shaped premaxilla, which extends upwards to meet the prefrontal. 

 The premaxilla is only loosely apposed to its fellow of the opposite side 

 below the narial opening, where the pair together form the characteristic 

 recurved beak, without any distinct trace of tooth - substance. The 



' Specimens in the Shrewsbury Museum arc marked S. with a numeral ; thof^e in 

 the British Miiseupi are marked B.M., fqllowed by s^ registev-nutnher. 



