101 



sideration, there is little iloiibt that the reptile was entombed lying on its 

 back. 



The texture of the bones is peculiar. There are nowhere to be seen 

 medullary cavities, and the bone is spongy, but very finely so; the tubules at 

 the largest being equal in diameter to an ordinary pin, and generally consid- 

 erably smaller. They are arranged in concentric series. There is no thick 

 dense layer of the bone as in other tortoLses, but an extremely thin one, 

 which is hard, and sculptured on the surface with minute grooves or pits. 

 The tissue of the bone is very fragile, and has si fracture like the mineral 

 inclosing it. Many of the bones, especially those of the dermal skeleton, are 

 extremely attenuated on the margins, being no thicker than writing-paper. 



In discussing the affinities of this genus, one doubtful point must be 

 considered. The large tlat elements described as lateral dermal bones, are 

 they ossifications of the dorsal or ventral integumentl They were found 

 below all the other bones, and nearly all the ribs laid on them with their 

 heads turned upward. This rendered it probable that the shields were 

 dorsal, and that the animal was entombed on its back; and a coracoid, which 

 was afterward found lying immediately on the largest bone (No. 10), crossed 

 in its course parts of two ribs. This could not have been the case had the 

 shields been ventral. An examination of the shields docs not reveal any 

 conformity to any known type of Testudinate plastron. The bones radiate 

 in all directions, leaving no margins for fore and hind limbs, or for a median 

 fontanelle, still less for suture with each other. 



Should these bones then be regarded as dorsal, they constitute a charac- 

 ter not previously noticed in the order, but one whose homologue is seen 

 probably in the dermal shield of bony tesselated plates seen in Sphargis. 

 The other points of affinity to Sphargis are the distinct ribs; the thin lamin- 

 iforni jaws with cutting-edges; the quadrate bone with such a strong anterior 

 concavity ; the elevated position of the zygomatic bone ; the form of the 

 humerus. Points of special reseml>lancc to Chelone are : the short posterior 

 superior portion of the quadrate ; the entire edge of the maxillary bone ; the 

 deep dentary. Tlie points in which it diffisrs from both are numcrou.s. 

 They are : the dorsal shields; the marginals; the notched symphysis, etc.; tlic 

 shortened articular end of scapula; the elongate form of the carapace, etc. 



The constant separation of (he ribs and the shortvertebrae are charac- 

 ters which arc more like those possessed by other reptiles Ihau (liose cliarac- 



