54 FOSSIL REPTILIA OP THE LONDON CLAY. 



clavicular process (58) is shorter than the scapula, and slightly expands at its extremity. 

 Both parts are longer and more slender than the homologous ones of the recent Trionyw 

 figured by Cuvier.* 



Fig. 5. The coracoid has the expanded, slightly curved form characteristic of the 

 genus ; it is not so broad as that figured by Cuvier. f 



Fig. 6 is the iliac bone, short, thick, curved, subcompressed, attenuated and 

 striated at its sacral extremity ; the enlarged articular end is divided into three 

 facets : two oblong and rough for sutural junction with the ischium and pubis ; one 

 smooth, and the smallest of the three, for the acetabulum. 



Fig. 7 is the almost entire right femur ; its convex, long oval head, bends inwards 

 from between the two trochanters, of which the external and largest is broken off. The 

 shaft bends backwards, and gradually expands to the feebly divided convex condyles. 

 All the characteristics of the modifications of the femur in the Trionyx are here 

 preserved. 



Fig. 8 is a claw-bone, natural size. 



Fig. 9 9' 9" are three views of the sixth cervical vertebra of the same Trionyx. 

 This may be recognised by the broad, depressed, posterior surface of the centrum, 

 partially divided into two cavities, side by side (c') ; the seventh cervical has the two 

 cavities there quite separated from each other ; the fifth and preceding cervicals have the 

 posterior surface of the centrum with a single cavity ; so that the sixth cervical is the only 

 one which has a single convexity in front (c, fig. 9), and a double concavity {c , fig. 9 ") 

 behind. The body is long, slender, compressed in the middle, with one median inferior 

 ridge anteriorly, and a pair of inferior ridges posteriorly ending in hypophysial tube- 

 rosities (fig. ^, yy), which support, as it were, the posterior articular cups. A short, 

 obtuse diapophysis projects from each side of the fore part of the centrum. The prezy- 

 gapophyses {z) support slightly convex, oblong, articular surfaces ; the zygapophyses 

 (/) are long, diverge, and support concave, oblong surfaces looking downwards. 

 There is no spine ; the neural arch is complete above the middle third of the centrum, 

 the canal expanding towards both its wide, oblique outlets ; this modification of course 

 relates to the great extent of motion between contiguous vertebrae, and the necessity 

 for providing against compression of the myelon during their rapid inflections and 

 extensions. 



The specimens of Tri. incrassatus here described are preserved in the Museum of 

 the Marchioness of Hastings, by whose kind and liberal permission they, with other 

 rare Chelonites, have been described and figured for the present Monograph. 



* Loc. cit., pi. 12, fig. 4. 

 t Loc. cit., pi. 12, fig. 4. 



