186 



957. The carapace of the same Trionyx. 



It consists of the centrums, neural arches, expanded spines and pleurapophyses of the nine 

 succeeding vertebrae, which are immoveably connected together, and are reckoned as dorsal 

 vertebrse. The first of these is remarkable for the large size and subspirally curved form of 

 the anterior zygapophyses : the pleurapophyses are short and slender, articulated by one end 

 to the sides of the expanded anterior part of the centrum of the first dorsal vertebra, and by 

 the other end to the costal plate connate with the rib of the second dorsal vertebra. The 

 nuchal plate is remarkably expanded in the transverse direction, and forms the anterior border 

 and first piece of the carapace, the major part .of which is composed of the expanded costal 

 plates connate with the pleurapophyses of the second to the ninth dorsal vertebrse inclusive : 

 the eighth pair of costal plates are articulated to each other by a suture at the median line, 

 behind the neural plate. The neurapophyses of the vertebrse of the carapace are moved for- 

 wards, so as to be articulated partly to the centrum in advance of their own. The pleur- 

 apophyses have undergone a similar displacement, and their depressed expanded heads are 

 articulated by suture with the sides of the contiguous ends of the two centrums. The cen- 

 trums are remarkably broad and depressed in most of these vertebrae. 



958. The plastron of the same Trionyx. 



It is chiefly remarkable for the peculiar chevron-shape of the entosternum, for the extreme 

 breadth of the hyo- and hypo-sternals, and for the expansion of the xiphisternals. 



959. The caudal vertebrae of the same Trionyx. 



Genus Chelys. 



960. The skeleton of the Matamata, or Fimbriated Tortoise (Chelys fanbriata, 

 Schweigger). 



The cranium and complex hyoidean apparatus of this species are figured and described 

 in the 'Ossemens Fossiles' of Cuvier, torn. v. part 2. 1824, pi. 11. figs. 21-25, and pi. 12. 

 fig. 41. The small wedge-shaped bone, hypapophosis, representing the so-called body of the 

 atlas, has been lost in the articulation of this specimen : the odontoid, which Cuvier rightly 

 describes as the body of the atlas, is here unusually developed, and supports by a sutural 

 articulation the major part of the atlantal neurapophyses : the suture by which these are 

 united together above the neural canal is still retained. The neurapophyses send out late- 

 rally short compressed diapophyses, and posteriorly, long subtrihedral zygapophyses. 



The second vertebra is much elongated, sharply carinate below, with larger diapophyses, 

 and with anterior as well as posterior zygapophyses ; the third and fourth vertebrse re- 

 semble the second, the centrum being convex in front and concave behind : the fifth vertebra 

 is convex, both before and behind : the sixth vertebra is concave before and presents two 

 convexities behind : the seventh vertebra has a corresponding double concavity in front, and 



