KJ 

 . The sixth conical vertebra of the same 



This is distinguished by two concave surfaces, placed tide by lido on the posterior |rt of 

 the orntrum. 



929. The seventh cervical vertebra of the same Trionyx. 



Thi* ha* two convexities on the fora part of the centrum, a* well as two concavities at the 



takpart. 



930. The eighth cervical vertebra of the same 



This has two convexities on the fore part of the centrum, but the back part has dwindled 

 into a thin, rough, obtusely-pointed edge, which is joined in the recent animal by rUv-tn 

 ligament to a corresponding rough depressed border, terminating anteriorly the centrum of 

 the first dorsal vertebra. The junction between the last critical and first dorsal is chiefly 

 effected by the sygapophysial joint*, a broad, deep, oblique concavity in the last cervical 

 being adapted to a corresponding but more extensive convexity on the first dorsal. The rapid 

 retraction of the head and neck is chiefly performed by the mowments between these two 

 vertebne. 



931. The carapace, with the first dorsal vertebra and the single lumbar vertebra, of 



the same Trioityt. 



. ^^ The carapace is composed, as in the genus Ckrlo*r (see No. 769), of a combination of 

 eight dorsal vertebne with the neural and costal dermal plates, but the marginal plates art 

 absent. The pleurapophyses of the first dorsal vertebra are short, curved, and expanded at 

 their outer extremities, which articulate with the under surface of the first costal plate. Tin- 

 first neural or 'nuchal' plate is much developed transversely, with a median inferior ridgi- 

 articulated by ligament to the conjoined summits of the neurapophyses of the first dorsal 

 vertebra, and united by a posterior sutural margin to the fore part of the second costal plate*, 

 and to the second neural plate. The neural arches of the seven succeeding vertebne are dis- 

 placed forwards so as to rest equally upon their own centrums and the next in advance : their 

 spinet are "tmnn't with the neural plates. The neurapophyses of the ninth dorsal vertebra 

 have nearly resumed their normal connexions, but the spine is obliterated by the median 

 union of the costal plates connate with the ribs of the eighth dorsal vertebra. The vertebra 

 succeeding the ninth dorsal, or the last of the carapace, has no ribs, and represents a lumbar 

 vertebra. The next two vertebra; have short and thick pleurapophyses joined together at 

 their distal extremities, and forming on each side a broad surface for thr attachment of thr 

 iliac bones. 



1)32. The sacrum of the same Trionyi. 



This is composed of the two vertebne which succeed the lumbar one. The sutures joiniup 

 the nrurapophyses to the centrums, and the ribs to the neurapophyscs, remain. The anterior 

 surface of the centrum is concave, the posterior one convex, in each of these vertebne. 



