GIANT TURTLE FROM QUEENSLAND LOWER CRETACEOUS.— LONGMAN. 29 



In the ectal view, shown in PL XII, the surface of the plate is 

 approximately flat, but in the centre a deep depression, scar and transverse 

 fracture mark a position where the limb-bones, had been crushed in during the 

 process of fossilisation. Except in the region of the furrows adjoining digital 

 areas, the ental side is convex in section through the short axis. The exposed 

 section on the left shows a number of diploic cavities. 



The possibility of this plate being regarded as a left hyoplastron not 

 suturally connected with its accompanying hypoplastron was at first considered. 

 The development of plastral bones in existing Chelonidm leaves at first large 

 vacuities between these portions on each side. These may be noted in the plastra 

 of newly hatched turtles, and the development is beautifully illustrated in W. K. 

 Parker's monograph on the structure and development of the shoulder-girdle 

 and sternum in the Vertebrata. 10 But the evident length of the completed bone in 

 comparison with the width presents difficulties here, and the dimensions and 

 contours also put out of court the probability of a united hyo- and hypoplastron. 

 The writer therefore suggests that the plate may be the centre and greater part 

 of the left side of a large entoplastron. Taking this view into consideration the 

 bone may be compared to the entoplastron of Archelon ischyros, figured by 

 "Wieland. 11 The dactyloid processes do not show correspondence, but here we 

 should expect diversity, and there is much variability in these even in the same 

 species at the present day. Assuming that the left of the fragment approximates 

 to the centre of an entoplastron, there is no sign of a nether tubercular process, 

 though the incomplete state of the plate does not warrant a statement that it is 

 absent. It may thus have no affinities with the peculiar T-shaped entoplastron 

 characteristic of the Protostegince. Taking for granted that the centre of the 

 bone is situated near to the left margin, an entoplastron about 4 feet in width is 

 outlined. Following out our comparisons, we find that the breadth of our large 

 C. my das is well over 2 feet in the entoplastral region ; but the contours of the 

 anterior plastral bones here give scope at the side for the fore-limbs, and this 

 cannot be imagined for the outwardly curved entoplastron of Archelon. But 

 Wieland has pointed out that a greater breadth and ' ' a quite orbicular form ' ' is 

 characteristic of Cretaceous turtles, and thus an extended entoplastron comes 

 within the compass of our proportions. Probably such a plastral bone occupied 

 a position less anterior than its homologue in modern turtles. 



Remembering the faulty allocation of fragments by more than one 

 authority in the past, the writer has some diffidence in thus definitely placing 

 this bone, but he has taken the view that the flatness of the plate and the presence 

 of such lateral and posterior dactyloid processes preclude the possibility of its 

 being a nuchal. 



10 W. K. Parker, Eay Society, 1868, pi. xii. 



"Wieland, Annals Carnegie Museum, vol. iv., No. 1, 1906, p. 11. 



