195 



second pair is supported upon strong trihedral neck, and articulated to the interspace of 

 the first UK! second dorsal vertebra : it become* connate, at the part corresponding to thr 

 tubercle, with thr first broad costal plate, which articulates by suture to the lateral margin 

 ">f the first neural plate, and to portion* of the nuchal and third neural plate* : the connate 

 rib, which ia almost lost in the substance of the costal plate, is continued with it to the an- 

 terior and outer part of the carapace, where it resumes its subcylindrical form, and articulate* 

 with the second and third marginal pieces of the carapace. The neural arch of tin- second 

 dorsal vertebra is shifted forwards to the interspace between iU own centrum and that of 

 the first donal vertebra: a similar disposition of the neural arch and spine and of the riba 

 prevails in the third to the ninth dorsal vertebrae inclusive. The corresponding seven neural 

 i are connate with the spines of those Tertcbrse, and form the major part of the median 

 of the carapace : the corresponding costal plates, anchyloscd to thr ribs, form the 

 medio-lateral pieces : the ninth, tenth, and pvgal plates, with the marginal plates of the cara- 

 pace, do not coalesce with any parts of the endo-skeleton. The bony floor of the great abdo- 

 bos, or ' plastron,' is formed by the luemapophysea and sternum connate with dermal 

 i plates ; forming, as in the preceding Orders of Ckrtonia, nine pieces, one median and 

 symmetrical, answering to the proper sternum, but railed 'entostemal '; and eight in pairs 

 of these the two anterior are termed ' epistemals,' the next two expanded pieces ' hyoeter- 

 nals," the succeeding pair ' byposteraals,' and the next contracted pair ' xiphisternaU.' Tin- 

 iliac bones abut against the pleurapophyses of the ninth, tenth and eleventh vertebra-, count- 

 ing from the first dorsal vertebra. Beyond these the vertebra, twenty-six in number, are 

 free, with short, straight and thick pleurapophrses, articulated to the sides of the anterior 

 expanded portions of the centrums. They diminish to mere tubercles in the twenty-first 

 caudal vertebra, and disappear in the hut three, which are anchylosed together. The neural 

 arches of the caudal vertebra are flat above and without spines. The strong columnar sca- 

 pula is attached by ligament to the first costal plate, and descends almost vertically to the 

 shoulder-joint, of which it forms, in common with the coracoid, the glenoid cavity. A strong 

 subcy lindrical process or continuation of the scapula representing the acromion bends inwards 

 to meet its fellow at the middle line. The coracoid continues distinct from the scapula, ex- 

 pands, and becomes flattened at its median extremity, which does not meet ita fellow or arti- 

 culate with the sternum. The iliac bones are vertical and columnar, like the scapula, but 

 are shorter and more compressed : they articulate, but do not coalesce, with the pubis and 

 ischium. The acetabulum is formed by contiguous parts of all the three bone*. The pubis 

 arches inwards and expands to join its fellow at the median symphysis and the ischium 

 posteriorly : it sends outwards and downwards a long thick obtuse process from its anterior 

 margin. The ischia, in like manner, expand where they unite together to prolong the sym- 

 physis backwards. The foramen ovale seu thyroideum is nearly circular on each side. 



In this specimen a portion of the carapace has been fractured and depressed : it has been 

 repaired by a growth of bone from the fractured margins, which have extended over the 

 horny covering of the depressed portion. 



The skeleton was articulated from a specimen 



Presented by ^fr. Cross, of the Surrey Zoological Gardens. 



2c2 



